The Early Development of the Pigeon's Egg. 27 



nucleus enters the cytoplasm of the egg of Ephedra trifurca. "As 

 it disintegrates, minute cells appear, which are believed to be the 

 joint product of the chromatin of the second male nucleus and the 

 chromatin of some of the jacket cells; these minute cells at least 

 foreshadow the endosperm of angiosperms, and may be called physio- 

 logical endosperm" (p. 290). 



This case of the second male nucleus in the cytoplasm of the egg 

 of Ephedra is exactly parallel with the case of supernumerary sperm 

 nuclei in the cytoplasm of the pigeon's egg. The case of "double 

 fertilization" or ''triple fusion" in the Angiosperms which is often 

 compared with polyspenny in animals, is not a parallel case ; for in 

 the "triple fusion" the second male nucleus unites with two polar 

 nuclei, one of which is sister to the egg. From this fusion the 

 endosperm is fonned which is believed to nourish the embryo. 

 Henneguy ('02) described the entrance of spermatozoa into the yolk 

 cells of Distomum hepaticum, and he regarded the yolk cells as 

 abortive Qgg cells. These are offered for the nourishment of the egg 

 and the condition is quite parallel to the "triple fusion" of An- 

 giosperms. 



Accessory Cleavage and Segmentation of Egg Fragments. — The 

 division of the supernumerary sperm nuclei and the "accessory 

 cleavage" present a problem of interest. In spermatogenesis, there 

 is no division of the nucleus after the formation of the spermatid. 

 So far as we know, the spermatozoa do not divide in any medium 

 in which they are normally found, except in the cytoplasm of the 

 egg. But in the case of physiological polyspermy, the spermatozoa 

 are in a medium where any of them that becomes the successful male 

 pronucleus will divide after union wi'th the female pronucleus. 

 Therefore, the supernumerary sperm nuclei in the egg cytoplasm 

 may divide. The accessory cleavage of the selachian's and bird's 

 Qgg is certainly comparable to the division of fertilized enucleated 

 fragments of the sea urchin's egg or nemertian egg. 



"Inwandering Follicular Cells." — Harper ('04) illustrates an 

 "inwandering follicular cell." (Harper, '04, PI. II, Eig. Y i). I 

 have found a large number of cells in the perivitelline fluid in the 

 egg represented in Chart II. Harper's figure does not show the 



