The Progress of Zoology. 255 



since the day of the patriarch's servitude, which our marginal 

 Bibles place at a date 3600 years antecedent to the present 

 time. The tailless cats of the Isle of Man and the tailless 

 poultry of Burmah are scarcely to be traced back to their 

 parentage, and have all the characteristics of true species as 

 far as their constancy of reproduction is concerned. In his 

 twentieth chapter Livingstone says, " Near Massangano I 

 observed what seemed to be an effort of Nature to furnish a 

 variety of domestic fowls capable of bearing with comfort the 

 intense heat of the sun. Their feathers were curled upwards ; 

 thus giving shade to the body without increasing the heat. 

 They are here named ' kisafu' by the natives, and ' arripiada/ 

 or shivering, by the Portuguese. There seems to be a tendency 

 in Nature to afford varieties adapted to the convenience of 

 man. For instance, a very short-legged species of fowl was 

 obtained by the Boers, who required one that could be easily 

 caught in their frequent removals. A similar instance of 

 securing a variety occurred in the short-limbed sheep of 

 America." Such things as these are matters of daily observa- 

 tion ; the question is, to what law are they subject, or, in other 

 words, what is the philosophy of their occurrence? If Mr. 

 Darwin had sent forth his book as a collection of data, instead 

 of as the statement of an hypothesis, there would have been 

 the same broad field for discussion, but with the advantage of 

 greater freedom ; for it is in vain to seek for the philosophy of 

 varieties until we have arrived at an unexceptional theory of 

 species, which we certainly have not, unless it be the vague 

 definition that a species is a congenital expression of all the 

 forces concerned in its production. Our conclusions for the 

 present are provisional, and each new conclusion arrived at 

 simply pushes the inquiry a stage farther back. The subject is 

 as much one for experiment as for inquiry into the accidents of 

 nature. The intermediate form between the horse and the ass is 

 a mule, which is infertile with another mule of the opposite sex, 

 and it is thenceforth concluded that all hybrids of a given class 

 are incapable of procreation among themselves. But M. Bouy, 

 of Angouleme, is reported to breed hybrids between the hare 

 and the rabbit by thousands for the market, and these leporines 

 are further stated to be fertile both with the hare and the rabbit, 

 and with each other. Some of these leporines have borne 

 young in the Gardens of the Zoological Society, but whether 

 they are of the first cross is at present unknown. The differ- 

 ences between the two types are many, yet they are rather in 

 degree than kind. The heart of the hare is nearly five times 

 the weight of that of the rabbit, the lungs are nearly four times 

 as heavy, the calibre of the trachea three or four times as 

 great. Furthermore, the period of gestation in the hare is 



