248 W. WALDEYER. 
pulex, on the contrary, it occurs in the stage with eight 
cells. . 
In the very brief note (‘ Ber. d. naturf. Gesellsch. zu Frei- 
burg.,’ Bd. iv. pt. 1, 1888), it is not stated how the fusion 
takes place, whether only the nuclear structures, or whether 
also cellular portions conjugate. The authors think that the 
cells arising from the copulation will become reproductive cells. 
In so far as the nuclear structures are obviously concerned 
in the process of copulation, the idea presents itself that the 
power of transmitting by heredity is to be looked for in the 
nucleus. In fact, after the publication of Hertwig and van 
Beneden’s researches on copulation—many soon made up their 
minds that the nucleus was to be regarded as the only carrier 
of the material substratum of heredity. O. Hertwig (98) must 
be mentioned as the founder of this view, followed then by 
KGlliker (108), and most recently by Weigert (202) in his 
excellent article, ‘“ Neuere Vererbungstheorie.” Kolliker 
especially has discussed in detail the reasons for and against, 
which are of importance in the doctrine that the nucleus is the 
transmitter of heredity. I recognise fully and completely that 
many and weighty reasons can be brought forward as to the 
importance which the nucleus has on the shape and re- 
generation of lower organisms;' but, nevertheless, I must 
point out, that as yet no very conclusive evidence has been 
furnished. 
This would be furnished if we knew, absolutely certainly 
for any form of spermatozoon, that no part of the protoplasm 
of the mother-cell entered into its constitution ; or that, even if 
the protoplasm did form part of it, the former did not accom- 
pany the latter in the process of fertilization. 
But we are not in a position, either in regard to spermato- 
genesis, or as to the analysis of the phenomena of fertilization, 
1 In order to cite one instance, I mention the beautiful researches of A. 
Grube on Stentor ceruleus (88). If a fragment of the nucleus remains 
in a portion, however small, cut off from this animal, this portion will grow 
into a perfectly normally formed Stentor, which will not be the case with 
a portion without a nucleus. Nussbaum (47) arrived at similar results in 
Gastrostyla vorax, an Oxytrichine. 
