94
APPENDICES.
pairing season in the larger Cetacea. The facts before him relating to the northern humpbacks led him to believe that their foetuses in June have a length of about 250 mm.; at the end of July of 500 mm.; in October of upwards of 2,000 mm.; and at the end of March or the beginning of April of from 4,000 to 4,500 mm. added:-
"If we place the pairing time at the end of April or in the month of May, which stands more nearly in harmony with the cited measurements, we can assume with great probability the period of gestation to be about eleven months or near one year."
liste.
APPENDICES.
LIST OF FETUSES OF SOUTHERN HUMPBACKS.* †
95
Sex and Length of Fœtus.
Race.
Locality.
He
mm.
1918, November 25
?
25
?
F
December 19
Female
152 Marble-bellied 229 407
South Georgia
No. 18 14
"
字
20
Male
circa 140
Black-bellied Marble-bellied
59
"
H
17
69
"
H
24
Female
280
J
TI
11
"
80
685
2
"
+1
81
Male
492
Female
610
Black-bellied White-bellied
11
PJ
588 470 685
#
#
Marble-bellied)
Black-bellied
33
16
15
"
"
11
17
11
94 196
158
189
217
228
" 288
cirou 768 circa 768
? ?
South Shetland (Morch).
This assumption tallied with Scammon's supposition that the humpback of the Pacific (M. versabilis, Cope) goes pregnant for about ten or twelve months; it has been regarded as well-founded by all subsequent writers, so far as I am aware. The further data, collected principally by Mr. Cocks and Professor Collett, although dis- closing one or two exceptional variations which are considered below, support Professor Guldberg's finding of a gradual increase in the size of the fœtus from the month of June onwards in the northern humpback.
In the following table a complete list of the fœtuses of the northern and southern humpbacks, with their localities, dates, lengths in millimetres, and sexes (when known), is given :-
LIST OF FETUSES OF NORTHERN HUMPBACKS,
"
11
1914, January 5
་་
7
บ
8
**
15
1910, February.
1
To these perhaps may be added:-
1898, March
10
? ?
"
11
470
...1,900
Varangerjord, Norway (Collett, p.619).
"
**
PUBLIC RECORD OFFICE
Reference :-
Lic. 885
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO
23 PUBLIC RECORD OFFICE, LONDON
1895, May 21
Date,
Sex and Length of Fratus
mm.
Locality and Authority.
70 Finmark (Collett, p. 619).
(Guldberg, Cocks). Varangerfjord (Guldberg).
21
"
(Cocka, " 18 in."). (Southwell," 19 in.")
Is the range given by Collett for June.
Finmark (Cooks, " 18 in."); dam with much milk. Varangerfjord (Sara, Guldberg).
(Cocks, " 18 in.")
Vardo (Guldberg).
1885, June 1
810
1888
Male
260
1
11
260
12
19
13
822
11
"
1887
21
Male
880
1
28
?
482
11
260 840
1886, July 1
Male
890
1879
6
200
+1
11
"
1887
15
Female
880
"
1888
24
485
11
#1
27
468
15
}}
1886
1884
28
510
11
95
" (end)
575
*
Vardo (Guldberg).
11
12
(end)
650
"
>
1899, August 9
Male
1,000
18
1,145
[5]
1888
21 circa
11
circa 885
21
914
1883
21
904
"
1883 October
1891, November 20
circa 1,500
1898, March 10
1898
10
"
1898
£894 11
10
1846, April (beginning)
1898, May 11
circa 210-600
(Cooks, "17 Norwegian in.")
Is range given by Collett for July.' Newfoundland (True).
Finmark, Vardo (Cocke, “84) in.”) (Southwell.)
Finmark (Collett, p. 619).
13
1,940 Norway, Stavangerfjord (Eschricht).
Christianiafjord (Collett, p. 619). 4,800 Finmark, Tufjord (Collett, p. 619). 8,800
Jarfjord
"
470
11
1,900
#
Varangerfjord (Collett, p. 619).*
4,450 Norway, Stavangerfjord (Eschricht).
4,700 Finmark, Varangerfjord (Collett, p. 620).
* ? wanderers from the South Atlantic.
The observations recorded in the above tables are plotted upon the chart‡ which accompanies this report. In this chart the vertical lines represent the correspond- ing months of the northern and southern hemispheres, the months being divided into days by lines 2 mm., apart where necessary, while the horizontal lines represent metres (on a scale of th). A gradual increase in the length of the foetus from May in the northern hemisphere (or the corresponding month of November in the south) is visible in the tables just given, and more readily apparent in the chart. That such a definite and regular increase takes place is clear evidence of the fact that effective pairing is normally restricted in each race to a particular part of each year; in other words, both northern and southern humpbacks have a definite sexual season. Judging from the corpora lutea found in the ovaries by Major Barrett- Hamilton (cf., No. 69, 20th December, with three, the highest number observed, etc.; see above at p. 84 for details) this sexual season is of a polycestrous character; the majority of the differences of size presented by nearly contemporaneous foetuses in both the north and the south are, therefore, readily explicable as the results of pair- ings at different dates within the limits of the sexual season.
The list of northern foetuses shows that specimens of about 200 mm. in length may be found from the month of May (at least) to 6th July; others from 300 to 350 mm. in length occur between 1st June and 15th July, while those of lengths ranging between 460 and 510 mm. are found from 28th June to 27th July. From this it would appear that foetuses of similar size may be found on any day within a period of at least six weeks; and, therefore, if we assume that foetuses of equal lengths are practically of equal ages, we may infer that the sexual season of the northern humpback is of at least six weeks' duration. Such a term would be about equal to that of the season of parturition, which, in the case of the northern hump- back, according to Mörch, falls in April and the neighbouring weeks.
The variations in size, coupled with the dates of the fœtuses examined at South Georgia might lead one to a similar view of the duration of the sexual season of each of the three forms of humpback found there. It is to be noted that Major Barrett- Hamilton's observations, although too few in number to lead to any certain con- clusion on such a matter, suggest that the foetuses of marble-bellied humpbacks are less developed than the contemporaneous foetuses of the white- or black-bellied var- ieties; possibly, therefore, the sexual season of the marble-bellied form opens later In this connexion we may than that of either of its associates at South Georgia. note that from Risting's paper it would appear that on the west coast of Africa parturition takes place before August, and this is substantially confirmed by
* The report made by the Tönsberg Company to the British Museum mentions a fœtus 5 ft. long 'obtained on 24th November, 1918, from one of two females 41 and 40-5 ft. long respectively.
This fœtus was apparently unusually large.
For a list of recently recorded fœtuses from African coast and South Georgia see Appendix III.
(p. 185).
Fig. 1: reduced to half of the size of the original.
Page 210Page 211
PUBLIC RECORD OFFICE
Reference :-
1 TT TT CO. 885
23 PUBLIC RECORD OFFICE, LONDON
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH-NOT TO
96
APPENDICES.
Lieutenant Strong's report. On the other hand, Mörch speaks of new-born calves at South Georgia at the commencement of the season, and he supposes birth to take place at some time in September or October. If, on the ground of Lieutenant Strong's report, we may venture to identify the west coast humpbacks with the black-bellied form of South Georgia (see above at p. 92), we may perhaps suspect, having regard to the evidence of the fœtuses, that the marble-bellied race is the one whose season of parturition reaches into the month of September at all events.
Before we can determine with any certainty the dates at which the sexual seasons of the various races of humpbacks open we must obtain a good deal of further information. For the southern humpbacks, further data from South Georgia and the neighbourhood, together with observations upon the fœtuses and new-born young of the African coasta, are much needed. So much turns upon the determination of the age of the smaller foetuses that it is greatly to be hoped that in the near future some inquiries into the earlier stages of embryonic development in the larger Cetacea will be instituted.
Mörch, following the scale given by the late Professor Guldberg, estimated the age of the small foetuses which he examined at South Shetland in February, 1910, at two-and-a-half months, and he supposed "impregnation, therefore, about the 1st of November "; he thus appears to have allowed from two to four weeks for the descent and segmentation of the fertilized ovum and the establishment of the embryo. In arriving at the estimates of the ages of the small fœtuses from South Georgia, given in my "Preliminary Memorandum"* on the papers of Major Barrett-Hamilton, assumed (1) "that the estimate of eleven months' gestation for northern hump- backs is well-founded, and that it applies to the South Georgia herds"; (2) that the length of the calf at birth is 15 ft.; and (3) that the rate of growth is equal through- 33 for out pregnancy. On this basis I calculated a series of "possible pairing dates the foetuses, and these dates fell between 8th November and 7th December, eight out of eleven dates being in November.
The first assumption is, as regards northern humpbacks, a generally held opinion, and, even when applied to those of the south, it is probably not far wrong, although personally I am now inclined to think that the period of gestation is more likely to be twelve than eleven months. The second assumption may require some modification so far as southern humpbacks are concerned; Mörch was informed of calves "about 12 ft. long" at South Georgia; and some females of 42 ft. in length are there pregnant, as against 45 ft., the minimum length of a pregnant female in the north. On the other hand, mention has been made of calves (two with one 'dam) each about 10 Norwegian feet long," seen of the Finmark coast, near Vardö, in 1886 (Cocks, Zoologist, June, 1887).
With regard to the third assumption, viz., that the growth of the foetus takes place at a regular rate throughout pregnancy (an assumption also made by others; see J. E. Hamilton, Belmullet Whaling Report, British Association, 1914, p. 20), I do not now think it well-founded.
In the first place, the earlier stages of embryonic development in the mammalia generally are characterized by their extreme slowness. Thus in the rabbit fully 10 per cent. of the whole period of gestation is occupied by the descent of the fertilized ovum into the uterus, and it is not until more than 22 per cent. of the whole period has elapsed that the first trace of the embryo is discernible (Marshall, "Vertebrate Embryology," p. 342, 1893). Major Barrett-Hamilton was able to determine the sex of the foetal humpback when its length was no more than 6 in. (smallest male fœtus 5-6 in.; smallest female foetus 11 in.); and Sars showed long ago (Forhand. Vidensk-Selskab. Christiania, 1880, No. 12, p. 17) that the generic characters of Megaptera were clearly recognizable in a male foetus little more than 200 mm. (8 in.) long. Such facts, I think, point to extremely slow (in comparison with other mammalia) growth in the early stages of foetal life; the first few months of intra-uterine existence seem to be dedicated to the perfecting of form and structure, while the later months are occupied by a vast, rapid, and, it may be, regular increase of size.
At present we possess no means of judging how long the preliminary develop- ment of the embryo takes. With regard to its subsequent growth, the data collected
* Appendix VI., p. 57
Some of the generic characters are readily apparent in a foetus 43 mm. long from New Zealand;
vide Lillie, "Terra Nova" Report, Zoology, vol. 1, p. 109, Pl. IV.. fig. 4, 1915.
APPENDICES.
97
from the foetuses suggests, but by no means conclusively, that gestation lasts for about nine to ten months after the establishment or preliminary development of the foetus. These data are summarized in the following table, and a study of this will show how badly further observations are needed before we can lay claim to any reliable knowledge of this difficult but important matter.
LENGTHS OF HUMPBACK FŒTUSES; SUMMARY.
Southern Hemisphere.
Northern Hemisphere.
Guldber," Scale.
Mouth.
No. Average. Ilange.
Mon b.
No. Average
Hange.
827
70 260-482
250
November 2 5 December
100 879
152 229 (marble-bellied)
May June
།སྦྲུ
I
July
8
448
200-650
500
January...
4
August September
Ꮌ .
960 885-1,145
1,000 February 2 1,500
March
27
October ... November
1,940 1,500
December
January...
February March
April
May
| 11 |
2,000 April
2,500
May
8,000 June 3,500 July
2 4,050 8,800- ef. Southern column.
...
1
4,450 4,700
4,000 4,800 4,500
Birtli.
August... September
October November
140-685 (marble-bellied, 140-280 and recent im- pregnation on Dec. 13, black-bellied 407-482).
562 470-685 (marble-bellied
470, black-ballied 685, white-bellied 689–610),
768 (?race),
1,185 470-1,900 Norway; but
? migrants from sonth.
768
of
(Birth: west
coast
Africa black-bellied race.)
(Birth supposed by Mōrch: ? marble-bellied race.)
In his description of the Greenland humpback, or Keporkak, Fabricius said:- "Parit vere (non autem annis omnibus) pullum solitarium, qui matrem sequitur usque donec successorum acquisit." This statement appears to be quite accurate.
The only instance of twin humpbacks is that recorded by Mr. Cocks (Zoologist, June, 1887), on the authority of Herr Wiborg and other whalers; these saw a female accompanied by two calves, each about 10 Norwegian feet long, near Vardö, on the coast of Finmark, in the summer of 1886.*
Risting states that Morten Ingebrigtsen, a whaler who has studied the hump- back closely, both in northern waters and off the west coast of Africa, is of opinion that the humpback only gives birth to young in alternate years. Certain of the whalers, however, think that the humpback has young every year, and that pairing, therefore, takes place soon after parturition; those operating in South Shetland support this view by saying that there they very rarely catch females which are not pregnant. Commenting on this, Risting points out that such nice researches are not commonly undertaken by whalers, and he is inclined evidently to favour Ingebrigtsen's view. In confirmation of Risting's comment one may cite Mörch's statement that "it is unfortunately only by the merest chance that observations Some of Major upon the period of gestation of the various species can be made.” Barrett-Hamilton's observations have a direct bearing on this important point.
Reference may be made to No. 126, a nursing black-bellied "female in which the one ovary seen was dormant and the uterus clean and apparently unimpreg- nated; to No. 48, a nursing marble-bellied female in which the one ovary seen had a large corpus luteum, the corresponding uterine cornu being folded and con- gested and containing some mucus appearances which led Major Barrett-Hamil- ton to say that " evidently there had been a calf suckling recently and recent impregnation"; and to Nos. 3, 13, and 251, the three in which some milk was present in the glands and in each of which there was a comparatively recent preg- nancy. The largest fœtus found in a dam with any milk present in her mammary glands was one of 6 in. (No. 18). The smallest fœtus found in a dam without milk was one of 5-6 in. (No. 69); and ten out of fourteen pregnant females examined * Three cases of twins are recorded from west coast of 'Africa by Olsen, see Appendix III. (p. 185).