82 



MALE PRONUCLEUS. 



embrace the former. The actual fusion does not take place till 

 after the pronuclei have been in contact for some time. While 

 the two pronuclei are approaching one another the protoplasm 

 of the egg exhibits amoeboid movements. 



The product of the fusion of the two pronuclei forms the first 

 segmentation nucleus (fig. 37), which soon, however, divides into 

 the two nuclei of the two first segmentation spheres. 



The phenomenon which has just been described consists 

 essentially in the fusion of the male cell and the female cell. In 

 this act the protoplasm of the two cells as well as their nuclei 

 coalesce, since the whole spermatozoon which has been absorbed 

 into the ovum is a cell of which the head is the nucleus. 



It is clear that the ovum after fertilization is an entirely 

 different body to the ovum prior to that act, and unless the use 

 of the same term for the two conditions of the ovum had become 

 very familiar, a special term, such as oosperm, for the ovum 

 after its fusion with the spermatozoon, would be very convenient. 



FIGS. 34, 35, AND 36. THREE SUCCESSIVE STAGES IN THE COALESCENCE OF THE 

 MALE AND FEMALE PRONUCLEI IN ASTERIAS GLACIALIS. FROM THE LIVING 

 OVUM. (Copied from Fol.) 



Of the earlier observations on this subject there need perhaps only be 

 cited one of E. van Beneden, on the 

 rabbit's ovum, shewing the presence of 

 two nuclei before the commencement of 

 segmentation. Butschli was the earliest 

 to state from observations on Rhabditis 

 dolichura that the first segmentation 

 nucleus arose from the fusion of two 

 nuclei, and this was subsequently shewn 

 with greater detail for Ascaris nigrove- 

 nosa, by Auerbach (76). Neither of these 

 authors gave at the first the correct in- 

 terpretation of their results. At a later 

 period Butschli (80) arrived at the con- 

 clusion that in a large number of in- FIG. 37 OVUM OF ASTERIAS 

 stances (Lymnaus, Nephelis, Cucullanus, GLACIALIS, AFTER THE COALESCENCE 



f ' OF THE MALE AND FEMALE PRONU- 



&c.), the nucleus in question was formed CLEI . (Copied from Fol.) 



