427
Annexe B.
REPORT ON THE RATS AND RAT-FLEAS FOUND IN HONGKONG.
Introductory.
To determine with accuracy the particular species of every rat arriving at the Public Mortuary is by no means easy. In by far the greater number of cases an opinion can be given with certainty, but there remain something like 20% which are difficult to recog- nise. This is due to several causes. (1) The young of both the common rats are very much alike, not only in size but in outline and colouring. The typical characteristics of the different species are only attained by the adult animal. (2) Some of the rats show the long ears of Mus rattus with the short coarse tail of decumanus. The possibility is that these nondescripts are hybrids.
Of late years considerable attention has been given to rats and some who have worked in this connection have been reluctant to give to every rat a place in any particular species. Captain W. G. LISTON, I.M.S., in a paper read before the Bombay Natural History Society in November, 1904, homologates the opinion that "It might be as easy to classify pie-dogs as rats in Bombay." A somewhat similar opinion is expressed by KITASATO in the Philip- pine Journal of Science, June 1906, where he states, when speaking of different breels of rats and their relation to plague: "Moreover the results of biological researches tend to confirm the fact that although two distinct species of rat are found, the one most prevalent in Japau is a race which is a mixture of the two.”
Species of Rats.
The following are the species of rats we have found in Hongkong:-Mus rattus, Mus decumanus, Mus musculus and the so called "musk rat" which is not a rat but a shrew "Sorex giganteus."
The black rat: Mus rattus.
Although this is usually called the black rat it is seldom that one is seen which is really black and we have not seen one of this colour in Hongkong. The most common colour is a dirty grey. The fur is usually fine and soft, of a lighter shade on the belly, and extends quite a little way along the beginning of the tail; mixed with the fur are sometimes a few spiney hairs, though these are often absent. The tail is longer than the body and head together, it is generally slender and papers to a fine point. The ears are moderately large, standing up distinct out of the fur and extending to the eye and even beyond it when laid forward. There are five pads on the fore foot and six on the hind foot. The hinder- most pads are elongated, the digits well separated and more delicate than in the decumanus. The claws are sharp, curved and adapted for climbing. The skull is slightly convex above. The incisors are exceedingly sharp and sloped on the wearing surface at a very acute angle. The inferior maxilla is broader, thinner and less rounded on its lower edge than that of the decumanus and the incisors follow the curve of its inferior border. The whole build of the animal is more light and graceful than that of the brown rat and is better adapted for climbing than burrowing.
The brown rat: Mus decumanus.
Taking an average
There is little to choose in colour between this and the black rat. of colouring the brown rat is the greyer of the two and of a lighter shade and this is more noticeable when a number of the two are examined together. The fur is coarse and on the back is mixed with longer and more bristle-like hairs which have a brownish red tint; these are continued on down the tail which is scaly and bare of fur almost from the root. The tail is shorter than the head and body together, it is thick and coarse, scaly and ends in a comparatively blunt point. In many specimens the point has been lost through some accident. The ears are short, rounded, set closely into the fur and when laid forward do not reach to the outer canthus of the eye. The feet are large and strong, the pads being more rounded than in the rattus and covered with a thicker, tougher skin, and the digits are shorter, stronger, more closely set together, and less finger-like than in the black rat. The claws are straighter, blunter, and coarser than in the rattus. The skull is more convex on the top than that of the black rat. The incisor teeth are more curved than