Mammalian Ova within a Uterine Foster-mother. 181 



Then again the Belgian Hare foster-mother had not ovulated when 

 the operation was performed ; ovulation in the rabbit does not take 

 place until about ten hours have elapsed after the act of coition, and 

 the operation was performed one hour or less after coition. 



It was quite possible then, that when ovulation did take plnce, 

 some nine hours later, some Dutch spermatozoa might still be 

 alive and in a condition to fertilise the Belgian Hare ova when they 

 were produced. 



Bat the Belgian Hare doe had been inseminated by a Belgian Hare 

 buck just before the operation ; and the spermatozoa from this buck 

 would arrive at the end of the fallopian tube before ovulation took 

 place ; this spermatozoa would be at least twenty-four hours younger 

 than the foreign Dutch spermatozoa, and both more vigorous and in 

 far greater numbers than the foreign spermatozoa. 



It seems to me that the possibilities are distinctly in favour of the 

 host of younger and more vigorous Belgian Hare spermatozoa beating 

 the comparatively small body of older and less vigorous foreign 

 Dutch spermatozoa, in the struggle for the Belgian Hare ova, but at 

 the same time it is possible the latter won, and that, in the case now 

 under consideration, these two badly marked young are the result of 

 a cross between Dutch spermatozoa and Belgian Hare ova. 



The only way to test this at all seemed to be by crossing the same 

 Dutch buck with Belgian Hare does, and comparing the offspring of 

 such crosses with the young foster-children. But even this could 

 not be conclusive proof no matter what result was obtained, for, as 

 is well known to rabbit breeders, although probably the majority 

 of offspring got by crossing two distinct breeds will be of a 

 nondescript character, yet cases continually occur where apparently 

 thorough-bred young, of one breed or the other or perhaps of both 

 breeds, are produced in the same litter together with obvious cross- 

 breds. 



However, I crossed this Dutch buck with two Belgian Hare does 

 and in the first case there were five young, one of which was Belgian 

 Hare purely in colour, two were coloured like a Belgian Hare with 

 white spots or patches here and there, one was black with a couple 

 of white spots, and one was white speckled with the characteristic 

 Belgian Hare brown colour. 



In the litter out, of the second Belgian Hare doe by this same 

 Dutch buck there were also five young, two of which were of pure 

 Belgian Hare colour, one was a light fawn colour mixed with a bluish 

 dun and with one white shoulder and fore leg, a fourth was a slightly 

 darker shade of the same colour with white fore feet, and the fifth a 

 very light fawn underneath, while somewhat darker on the back and 

 with white fore feet and white dash on the tail. 



None of the ten young produced in these two cross-bred litters at 



