Sessional_Paper_1902 — Page 839

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As to the relative prevalence of the three species of Anopheles, I am not able to speak as regards the 294 Anopheles which I received during the last quarter of 1900, but of 875 received during the three quarters of 1901 included in this research, 483 were Anopheles Sinensis, 249 Anopheles Macu- latus, and 143 Anopheles Minimus.

10. I have differentiated twelve species of Culex, which I describe at length in the Appendix. There are probably considerable more, as some of the varieties of certain species which I describe may be regarded by entomologists as distinct species. I do not attempt to follow THEOBALD in his new classification of mosquitoes, just published in the Tropical Journal, into twenty-four different genera, breaking up the old genus Culex into some twenty new genera, based on the arrangement of the scales which cover the insects. For instance, he now decribes Culex Scutellaris and Culex Obturbans, two of the most common of the Hongkong mosquitoes, as Stegomyia Scutellaris and Armigeres Obturbans. Culex Fatigans, Culex Scutellaris, Culex Obturbans, and Culex Concolor have been described before. Culex Anulus, Culex Scriceus, and Culex Reesii are new species, and have been named by Mr. THEOBALD from specimens which I submitted to him. Culex Reesii he has so called from our mutual friend Dr. D. C. REES, lately Superintendent of the London School of Tropical Medicine, who put me in communication with Mr. THEOBALD. The insects which I have indicated by the letters, "n", "o", "p", "r", "r", and "s", I, have carefully described, but not named. "p" may be Culex Fuscanus; the others are, I think, new species but this question I shall remit to Mr. THEOBALD at the British Museum.

Culex Scutellaris is the black and white striped mosquito so common all over the Colony during the day time; Culex Fatigans and Culex Reesii are the equally common brown mosquitoes, to be found everywhere and at all seasons in the evening; Culex Obturbans is the very large dark mosquito, also very widely prevalent. The others are less abundant, but for the most part occur pretty generally throughout the Colony.

It may be noted in passing that Culex Fatigans is the most usual intermediate host of the blood parasite, Filaria Nocturna, the cause of Elephantiasis and its kindred diseases, by no means uncommon. in this locality.

While Anopheles as a rule only use for breeding purposes clean water in more or less natural collections, the various species of Culex lay their eggs wherever stagnant water exists, in broken dishes, empty tins, flower pots, water tanks or barrels, drain traps, and the like. Nothing is too dirty to have its appropriate mosquito developing in it. Culex Obturbans is the most loathsome of all in its larval state, finding its most favourable conditions in decomposing urine.

11. I do not propose to enter here into details of prophylaxis against these insects, which I have dealt with in special reports: but direct attention to certain observations which I made during the

winter.

I found the larvae of Anopheles in the nullahs throughout the whole winter, in scarcely diminished. numbers, though there were few in the pupa stage, and development at that season is evidently very slow or arrested.

I was able to note the effects of severe cold at the beginning of February. On 1st February, I had made a careful examination of the Kennedy Town nullah, and found Anopheles larvæ plentiful. On the 3rd there was a sudden rapid drop in the temperature, and when I examined the stream again on the 5th there were few larvæ to be seen. It seemed as if they had been killed by the cold. But for- tunately I had some larvæ under observation at the time in a glass jar in my verandah. Under the influence of the cold these became torpid or sluggish, and most of them seemed dead. On the 7th, however, the sun shone out brightly, and the seemingly dead ones as well as the others became quite lively again. It is probable, therefore, that much of the diminution in numbers of the larvæ in the ravines during the winter is more apparent than real, since they are most easily recognised in ordinary circumstances by their very characteristic movements when disturbed.

I have the honour to be,

Sir,

Your obedient Servant,

Dr. J. M. ATKINSON,

Principal Civil Medical Officer,

&c.,

&C..

&c.

JOHN C. THOMSON, M.D., M.A.