252 HAND-BOOK OF PHYSIOLOGY. 



It has been often observed that a well-bred bitch, if she have been 

 once impregnated by a mongrel dog, will not bear thorough-bred puppies 

 in the next two or three litters after that succeeding the copulation with 

 the mongrel. But the best instance of the kind was in the case of a mare 

 belonging to Lord Morten, who, while he was in India, wished to obtain 

 a cross-breed between the horse and the quagga, and caused this mare to 

 be covered by a male quagga. The foal that she next bore had the dis- 

 tinct marks of the quagga, in the shape of its head, black bars on the legs 

 and shoulders, and other characters. After this time she was thrice cov- 

 ered by horses, and every time the foal she bore had still distinct, though 

 decreasing, marks of the quagga; the peculiar characters of the quagga 

 being thus impressed not only on the ovum then impregnated, but on the 

 three following ova impregnated by horses. It would appear, therefore, 

 that the constitution of an impregnated female may become so altered 

 and tainted with the peculiarities of the impregnating male, through 

 the medium of the foetus, that she necessarily imparts such peculiarities 

 to any offspring she may subsequently bear by other males. Of the direct 

 means by which a peculiarity of structure on the part of a male is thus 

 transmitted, nothing whatever is known. 



As bearing upon this subject, the following note kindly given to the 

 Editors by Mr. 8. Probart may be added: On the Farm Wellwood, the 



property of Charles R , Esq., in the Division of Graaff Remet, Cape 



of Good Hope, there is at present running an aged mare with a numer- 

 ous progeny. Some years ago she foaled for three successive seasons to a 

 donkey; after that she gave birth to a mare foal, to a horse. This filly 

 was a chestnut, and did not exhibit any taint of the donkey by which her 

 dam had previously foaled. But when she in her turn foaled to a horse, 

 her young bore the distinct marks along the back and withers, and rings 

 round the lower parts of the legs, which are the peculiarity of the ass and 

 the mule. Three foals she has had are all so marked. 



DEVELOPMENT. CHANGES IN THE OVUM UP TO FORMATION OF THE 



BLASTODEKM. 



The earlier stages in development are so fundamentally similar in all 

 vertebrate animals, from Fishes up to Man, that the gaps existing in our 

 knowledge of the process in the higher Mammalia, such as man, may be 

 in part, at any rate, filled up by the more accurate knowledge which we 

 possess of the development of the ovum in such animals as the trout, frog, 

 and fowl. 



One important distinction between the ova of various Vertebrata should 

 be remembered. In the hen's egg, besides the shell and the white or al- 

 bumen, two other structures are to be distinguished the germ, often called 

 the cicatricula or ' 'tread," and the yelk enclosed in its vitelline membrane. 



The germ is essentially a cell, consisting of protoplasm enclosed in a nu- 

 cleus and nucleolus. It alone participates in the process of segmentation 

 (to be immediately described), the great mass of the yelk (food-yelk) re- 

 maining quite unaffected by it. Since only the germ, which forms but a 

 small portion of the yelk, undergoes segmentation, the ovum is called 

 meroblastic. 



