KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 263 
somes). It provides only these two loops for the first segmen- 
tation. ‘Che number of loops, too, in the male pronucleus is 
reduced to two. Thus in fact the latter is the complement of 
the female, since both taken together have four chromosomes 
to form a “ complete nucleus ;” whereas each taken singly re- 
presents, so far as the number of loops is concerned, only “ half 
a nucleus” compared to the body-cells in Ascaris. 
The three theories mentioned have evidently only claim to 
full value if we are right in neglecting the protoplasm entirely 
in the act of fertilization. 
Since we have before us, in the process of fertilization, a 
process which is common to animals and plants, and has essen- 
tially the same significance in both, the work of botanists 
must be considered to some extent. I will, therefore, in con- 
clusion, give Strasburger’s view, who in this department has 
made the most observations amongst botanists. 
In his comprehensive work (193) Strasburger states that in 
the higher plants a fusion occurs; “ Sperm-nucleus and egg- 
nucleus lie close together, the nuclear membrane becomes lost 
at the point of contact, and the contents of the two nuclei 
unite to form a single one. It can be proved that by this 
process a mixing of the nucleo-plasm of the two nuclei is 
brought about and the nucleoli of the two nuclei also are 
usually seen to fuse with one another.” In opposition to this 
statement, I must not leave unmentioned the fact, strongly 
emphasised recently (191) by the same author, that in the 
resting nucleus the threads are not fused, but always consist of 
the same number of segments as appear during division. This, 
it seems to me, is greatly in favour of van Beneden’s opinion, 
that fusion is unnecessary. 
Strasburger believes that the different views of the process 
of fertilization can be brought under one head if it be granted 
that the union of the nuclei takes place at different stages 
of development in different instances. ‘Thus in Ascaris 
megalocephala the union occurs in a late stage of mitosis, 
when the segmentation-spindle is formed. In Echinoderms, 
however (Strougylocentrotus, as observed by the Hert- 
VOL, XXX, PART 8,—NEW SER. 8 
