LITERATURE. 3 



and that the first polar cell, though it could change its shape and also 

 vary in size, remained at the spot where it was formed. 



Holl's paper (1893) dealt with the formation of chromosomes from 

 the nucleolus. He made the number eighteen. Unfortunately, his ma- 

 terial was so poorly preserved that his results are unreliable. 



Sobotta (1895), who studied a large number of eggs (1402), stated 

 that only one polar cell was formed in about nine-tenths of the eggs — 

 a larger proportion than maintained by Tafani — while in the remaining 

 one-tenth two were formed. Those eggs which abstrict only one polar 

 cell are set free from the ovary in the stage of the germinative vesicle 

 or of the early prophase of the first maturation spindle. This spindle 

 is formed from the germinative vesicle after the egg reaches the ovi- 

 duct. Just before the polar cell is cut off the spindle becomes radial in 

 position. 



In the other tenth of the eggs (those forming two polar cells) a first 

 spindle is formed in the ovary 24 hours before ovulation. He does not 

 say how it is formed, but emphasizes the fact that it lies deep in the 

 egg and is twice as large as the spindle of eggs which produce but one 

 polar cell. The chromosomes also are different from those of the single 

 spindle. The division of the spindle which accompanies the abstriction 

 of the polar cell in the ovary is only rarely seen. Then ovulation occurs, 

 and, while the ovum is in the oviduct, the second spindle arises from the 

 chromosomes remaining in the egg. This spindle is exactly like the 

 single spindle of eggs forming but one polar cell. Consequently, in those 

 eggs which produce a single polar cell, it is the first spindle and polar 

 cell that are suppressed, the polar cell that is formed being the equivalent 

 of the second polar cell of eggs that form two. In all spindles the chromo- 

 somes number twelve and divide transversely. There are no centrosomes 

 nor polar radiations. 



In a later paper Sobotta (1899) describes and figures the division 

 of the first spindle. He emphasizes its large size and deep position in the 

 egg and the infrequency of this stage. He believes that the spindle axis 

 turns from a tangential position, and, just before the cutting off of the 

 polar cell, becomes radial, with one pole lying in the protuberance which 

 will become the polar cell. He further says, in correction of his earlier 

 statement, that the second spindle may be formed immediately before 

 ovulation. 



Gerlach (1906) agrees with Tafani and Sobotta that some eggs 

 produce one polar cell, others two; but in his opinion the proportions 

 are as three to one. He describes the origin of the first spindle, the 

 chromosomes (twelve in number), and the formation of the first polar 

 cell. This cell and the second spindle may be formed either in the ovary 

 or in the oviduct. Consequently ovulation may occur at any time from 

 the stage of the first spindle to that of the second. According to his 

 view, eggs in the oviduct with no polar cell must have the first spindle. 



