ake bs er ae a oe TE es OEN ee 
1885.] Zoölogy. TA 
still be the equivalent of a cell. This may be true, for instance, 
says Kölliker, for trematodes ; but he has shown that for the higher 
vertebrates the spermatozoa are, in toto, nuclei. It therefore 
follows that in the spermatozoa of lower animals the nucleus i is 
the necessary fertilizing part, the flagellum serving merely as a 
locomotor organ, being later absorbed by the yolk. The pollen 
grains of phanerogams are also nuclei. 
(6) The phenomena of fertilization : 
Since Bütschli, in 1872 discovered the two pronuclei in the 
newly fertilized egg, the phenomena of nuclear conjugation have 
been carefully studied, especially by O. Hertwig, Fol, and Van 
Beneden. It is agreed that the male element penetrates the yolk 
and unites with a portion of the egg-nucleus; but in some im- 
portant details there is disagreement. The most complete obser- 
vations have been made on Ascaris megalocephala by Van Beneden 
and by Nussbaum. These observers agree that only the nucleus 
of the zoosperm forms the male pronucleus ; though Van Beneden, 
even here, finds a “ perinuclear zone” which takes no part in the 
fertilization. It is also agreed that before being fertilized, or con- 
jugating with the male pronucleus, the egg-nucleus throws offa 
portion of itself in the polar globules, by a complex | process re- 
sembling indirect cell division. In this process it is generally 
agreed that the nuclear figure is divided equatorially; but Van 
Beneden strongly insists that the division is meridional. He 
further thinks the germinal vesicle is not an ordinary cell nucleus 
because a% the chromatin is in the nucleolus 
Minot, Balfour and Van Beneden think all cells are herma- 
phrodite; and that before conjugation can take place the male. 
cell must lose its female nuclein, and the female cell its male nu- 
clein which is passed over into the polar globules. But against 
such an hypothesis there are grave objections. 
(1) It is known that in the processes of spermatogenesis in many 
animals, no part of the spermatogonia is lost. (2) Usually two 
polar globules are successively formed by the repeated halving 
of the egg nucleus. Now to get rid of the male nuclein this sub- 
stance must be so distributed as to be separated by the plane of 
division from the remaining or female nuclein; and then, the 
male nuclein would be lost in the first globule and there would 
be no need of a second. (3) We know that the spermatozodn 
confers hereditary traits from both father and mother upon off- 
spring ; and likewise for the female pronucleus. Therefore we con- 
clude, the pronuclei are essentially tn their nature hermaphrodite. 
Kolliker plausibly suggests that the function of the polar glob- 
ules is simply to reduce the size of the egg-nucleus comparable to 
that of the male pronucleus. 
1 This word, h: rodite, means pami that hereditary powers from two pies 
of ancestry, indefinitely dichotomously: co unded, are combined, and not what w 
popularly understand by the term.— oats : 
VOL. XIX,—NO, XII. 80 
