VIVIPAROUS FISHES OF THE PACIFIC COAST. 
445 
Balbiani has suggested that the yolk nucleus supplies the place of the sperma- 
tozoa in the case of the parthenogenetic eggs. I do uot know whether it has been 
found in parthenogenetic eggs or not, but will venture a suggestion.* If, as I sup- 
pose, this yolk-nuclear element corresponds to the macronucleus of protozoa, we may 
imagine a condition in some eggs in which the macronuclear elements or ontogenetic 
elements, and the micronuclear element or the phylogenetic elements are evenly bal 
anced. In such eggs the macronuclear element (the ontogenetic element) could provide 
for continued growth and division which in eggs in which the micronuclear element 
predominates is only provided by the union with the male. The micronuclear element, 
on the other hand, could provide for the building up of the ancestral form. This 
explanation seems sufficient to account for parthenogenetic eggs. It is desirable now 
to reexamine parthenogenetic eggs with this hypothesis in mind. 
The notices of this body in literature have been mostly at haphazard. This or 
that author says: “I have seen it,” and another has given its origin in one egg, while 
another has endeavored to explain its function in still another. While the literature 
bearing on this subject is largely incidental, enough has been said to show its presence 
in such a variety of animals that only a deep rooted explanation is sufficient. 
That the yolk nucleus is the lineal descendant of the macronucleus may be 
doubted. Both are probably similar results due to similar causes. It is certain that 
the germinal epithelial cells contain both the functions of the micro and the macro 
nucleus. How have the nuclear substances presiding over these different functions 
become united in a single nucleus in metazoa * 1 ? The answer seems evident. Both 
micro and macro nuclei are derived from a single nucleus. In protozoa they are the 
product of the second segmentation of the conjugation nucleus. We have here a single 
segmentation between copulation and macronucleus, whereas in metazoa a large 
number of segmentations intervene, and in this lies the chief difference. (Two more 
segmentations intervene in the case of spermatozoa than in the case of ova.) Macro 
and micro nuclear substances are both found in the germinal epithelial cells because 
the substances have not yet been separated. 
Which of the two second generation nuclei becomes the micro, which the macro 
nucleus is determined by their position anterior or posterior in the new infusorian. 
Bambeke in Scorpcena scrofa L. There are other minor points of difference that will appear on reading 
the two accounts. 
I have given this full statement of Henneguy’s theory to avoid any possible claim of injustice on 
my part to the propounder of a theory, which in so many points agrees with mine. S-pace and time 
do not permit me to consider Bambeke’s paper and one by Dr. O. Jordan, 1893. It seems, however, that 
Jordan has entirely underestimated the significance of the yolk nucleus. It may be true that 
structures in certain eggs have been described as yolk nuclei, which were not homologous with the 
yolk nucleus of Cymatogaster and of other fishes, or of Batrachians. But this does not warrant the 
sweeping statement that “ the various structures usually grouped together under the name Dotter- 
kern have nothing but the name in common.” This seems but trifling with facts. I have explained 
why the yolk nucleus may not become visible in one species and be present in another closely allied 
species. The absence is apparent rather than real. But supposing its absence should be real in 
some cases, that would not in the slightest vitiate the importance of a structure whose wide distribu- 
tion in metazoa is admitted. “Certain fishes do not have ventral fins, and some mammals do not 
possess posterior limbs, but these facts do not destroy the homology of ventral fins of fishes which do 
possess them with the posterior limbs of mammals which have these structures. The three papers 
mentioned in this note give a very complete history of the literature bearing on the yolk nucleus. 
* Balbiani’s yolk nucleus is not homologous with the structure here considered, and his view is, 
therefore, not identical with the one here given. 
