XCU GENERAL INTRODUCTION. 



been known to suckle offspring not their own. At the 

 same time I am free to acknowledge that many cases of 

 strong evidence in favour of the fertility of mule mares 

 have come before us." After referring to a case he had 

 just heard of in Mexico, he proceeds to say, ''This is one 

 of the most detailed accounts of a fertile mule that has 

 come under my notice.'^ Mr. Tegetmeier, it will be 

 .observed, does not say what he actually thought as to 

 the genuineness of any of the cases he had recently 

 heard of, but it may be inferred that in 1897 he was less 

 sure mules were invariably sterile than he was when 

 the work ' Horses, Asses, and Zebras ' was published in 

 1895. As " little scientific observation has been brought 

 to bear upon the question of the character of the hybrids 

 between the horse and the ass," I shall now state shortly 

 the results of recent observations on the reproductive 

 system of two female zebra mules, or, to be more 

 accurate, of a female zebra mule (zebrule) and a female 

 zebra hinny (zebrinny). 



In my zebra-horse yearling hybrid, Heckla, which died 

 recently, the reproductive organs were found to be almost 

 identical with the corresponding organs in a young 

 Burchell zebra (which died about a year ago), and unlike 

 in various respects those of a mare. Heckla thus in- 

 herited her reproductive system through her sire, not from 

 her dam, the Iceland pony. In a ten-year-old horse- 

 zebra hybrid which also recently died I found the repro- 

 ductive system resembled that of Heckla, but there was 

 this important difference, that one of the reproductive 

 glands contained one large and several small Graafian 

 follicles which closely agreed with the follicles in the 

 reproductive gland in the mare, and were, as far as I can 

 make out, identical with the germ sacs or follicles in a 

 six-yeav-old Burchell zebra. One of these follicles had a 

 diameter of 1^ inches, — a ripe follicle in a sixteen-hands 

 mare has a diameter of about If inches. From the ap- 

 pearance of the follicle it may very well have contained a 

 nearly mature germ-cell (ovum). 



While it may be safely inferred male germ-cells almost 



