48 THE MATURATION OF THE EGG OF THE MOUSE. 



Through the kindness of Professor Coe, of Yale University (Dr. 

 Kirkham being abroad) , we had the privilege of examining a portion of 

 Dr. Kirkham's preparations, some 25 slides, on which the position of 

 eggs with first polar cell and second spindle and that of eggs with a 

 single spindle had been marked by the author. An examination of these 

 preparations revealed the fact that nearly all of the ovarian eggs so 

 marked were in process of degeneration. They were of about normal 

 size, but occurred in rather small follicles, approximately like the one 

 shown in Kirkham's (19076) plate V, fig. 11. The zona pellucida was 

 gone, and the granulosa cells were only rarely in contact with the egg — 

 sure signs, in our opinion, of degeneration. Such eggs can be found in 

 nearly all ovaries; but we have always rigidly excluded them, because 

 they are so obviously different from the normal eggs contained in the 

 large follicles. Sometimes in these small follicles there can be found 

 clusters of cells resulting apparently from the abnormal cleavage of de- 

 generating egg cells. These facts explain, we think, fig. 7 of Kirkham's 

 second paper (19076), a figure which Sobotta (1908, p. 260) could not 

 understand, and also fig. 11 of the same paper, which is clearly that 

 of a degenerating egg. Kirkham (19076, p. 77) says, in explanation of 

 the absence of the zona from this and all other eggs of the same series 

 (presumably the same animal), that it is "probably due to the solvent 

 action of the killing fluid." But it certainly would be remarkable if 

 the same killing fluid operated so differently on different ovaries. The 

 explanation which we have suggested — a degenerating condition of the 

 ova — is rendered still more probable by the fact that "all the ovarian 

 eggs in this series are likewise naked." Tafani (1889, p. 24) in his criti- 

 cism of Bellonci expresses the opinion that the latter saw in degenerating 

 follicles eggs which never would have been set free, but which formed 

 polar cells. Such eggs are just what Bellonci, having little material, 

 would probably have seen and misinterpreted, for the reason that they 

 occur in all ovaries of mature mice at all times, whereas normal eggs con- 

 taining the first spindle or the first polar cell and second spindle can be 

 found only during a very limited period. However, it must be borne 

 in mind that, while Tafani did not misinterpret degenerating eggs, he 

 did confuse the first and second spindles. He saw the first spindle in 

 the ovarian egg, but apparently not the formation of the first polar cell, 

 and seeing a spindle (the second) in eggs in the oviduct without the first 

 polar cell, he mistook it for the first spindle. That he missed the stage 

 of the abstriction of the first polar cell is rendered the more probable 

 by the fact that he placed the period of maturation rather late and studied 

 so many eggs from the oviduct. Nevertheless, Tafani's criticism of 

 Bellonci was probably sound. 



There are apparently no statements in any of the works on the em- 

 bryology of mammals which show precisely how much time is required 

 for any part, or the whole, of the maturation process. Indeed, the 



