244 
H. E. Jordan 
The more important results of this study , apart from a description 
of the grosser features of maturation and fertilization, concern the 
negative evidence respecting the hypotheses of the individuality of 
the chromosomes and the geuetic continuity of the centrosome. 
Cumingia thus ditfers from the eulamellibranch, Zirphaea, described 
by Griffin (’98) wliere both the chromosomes and the centrosome are 
said to retain their identity throughout the oöcyte history. 
Chromatin and Chromosomes. 
The primary oöcyte at the beginning of the growth period has 
a nucleus of 3 microns diameter with an achromatic reticulum and 
a deeply- staining spherical nucleolus (Fig. 1). No mitoses could 
ever be found in the ovary, hence the oögonial stages must be 
sought for in the embryo, as perhaps also the synapsis. The attempt, 
however, would probably be barren of results for, judging from similar 
stages in the spermatogenesis, the cells would be far too minute for 
accurate observations. 
Accordingly , the study of one of the most interesting and im- 
portant Problems of germ-cell history; namely, the method of chro- 
mosome reduction, is practically impossible in the case of Cumingia. 
Nor does the matter appear much better with Zirphaea or even 
Thallasema (a gephyrean described in the same paper), or any egg 
in which synapsis cannot be definitely observed following the last 
oögonial mitosis and resulting in bivalent chromosomes which can 
be traced through the growth period into the first polar spindle. The 
important fact at this stage is the complete absence of chromosomes 
as such (chromatic bodies) or even of extra-nucleolar basichromatin in 
the germinal vesicle. 
A slightly later stage (Fig. 2) differs from the forcuer only in 
size and the presence of several chromatic masses (exclusive of the 
nucleolus) in the nucleus. At a still later stage (Fig. 3) the nuclear 
reticulum contains a number of longer and shorter chromatic bodies 
wich now appear for the most part rod-like anb arranged in pairs. 
Similar appearances in various forms have been regarded as indi- 
cating a side to side union of chromosomes. If one accepted the gene- 
ralization of the Schreiners that synapsis invariably takes place by 
sideto side union, this might be interpreted as parasynapsis. Meves (’08) 
however, has pointed out that this generalization rests upon faulty 
evidence obtained in part from an incorrect seriation of stages in the 
