W. B. Kirkham — Maturation of the Egg of the White Mouse. - 69 



polar bodies are always formerl, and the eggs leave the ovary with 

 the first polar body and the second polar spindle fully formed. 



Marshall and Jolly (:05) have determined that in the bitch ovula- 

 tion occurs independent of copulation. 



Rubaschkin (:05) finds that in the guinea-pig ovulation takes 

 place a short time after pai'turition (not immediately after, as stated 

 by both Bischoff ('52) and Reichert ('61) ), and is independent of 

 coitus. The first polar body and the second polar spindle are 

 formed within the ovary. The second polar body is always formed 

 after the egg is fertilized, the spermatozoon entering the egg in the 

 lower pavt of the Fallopian tube or in the upper end of the uterus. 

 Eggs which fail to be fertilized degenerate with the second polar 

 spindle. 



Heape (:05) has worked with rabbits, and finds that ovulation 

 occurs about 10 hours after copulation, as stated by Barry ('39), 

 but the eggs degenerate within the ovary if there is an insufticient 

 supply of blood to that organ, or if the male is withheld during 

 oestrus. According to this observer, maturation takes place about 

 nine hours after copulation, two polar bodies being rapidly formed 

 within the ovary. In this respect, the rabbit's Qgg is different from 

 all other mammal qq-qs, thus far studied. If the buck is withheld 

 from the doe during several consecutive periods of oestrus, most, if 

 not all, of the older, and many of the younger, follicles undergo 

 degeneration, and this may result in more or less persistent sterility. 



A survey of the literature therefore indicates that, while there 

 are many variations as to the details of the process, all mammalian 

 eggs which have beep carefully studied (with the exception of that 

 of the mouse alone) agree with those of practically all invertebrates 

 in the formation of two polar bodies. As a result of the foregoing 

 studies, the Qg^^ of the mouse, although subjected to more extensive 

 examination than that of any other mammal, seems to stand out 

 sharply as an aberrant type, in that it has been said to form but a 

 single polar body in from 75 to 90 per cent, of the eggs observed. 



With a view of determining the cytological nature of these 

 apparenth^ abeiTant maturation processes, the writer has recently 

 made further investigations on the egg of the white mouse, the results 

 of which are described on the following jiages. 



II. — The Egg of the Mouse. 



Material and Method. — To obtain the material. for this series of 

 investigations, the method used was as follows : During the active 

 breeding season when the adult females, as a rule, are in heat every 



