A cytological study of the egg of Cumingia with special reference etc. 247 
somes, the result of a transvers Splitting of halves of the original bi- 
valent chromosomes. The memhers of these pairs are simply separated 
in the second mitosis. 
Figures 18 and 19 illustrate the formation of the first polar hody 
and the second polar spindle. Suhsequent stages of the second 
maturation phase are shown in figures 20 to 25. The important fact 
up to this point as far as the chromosomes are concerned is, that, 
excepting in the heteroptypic mitosis, the chromosomes have always 
had a short rod-like shape. Following the late telophase stage (Fig. 25) 
when the chromosomes of the central pole are still rod-shaped and 
appear enclosed by a delicate membrane, a stage ensues where the 
chromosomes have given origin to a number of small vesicles with 
metachromatic reticulum (Fig. 26). These several vesicles (one for 
each chromosome?) subsequently coalesce to form two larger vesicles 
with chromatic reticulum (Fig. 27) and these ultimately fuse to form 
the definitive female pronucleus. 
Thus far then the individuality of the chromosomes has heen 
several times lost: 1) in the young primary oöcyte; 2) in the chro- 
mosome-mass of the growing period; 3) in the female pronucleus. 
There is here apparently no persistent identity of the chromosomes 
as such as described for Zirphaea and Thallasema^ i. e. as masses 
of chromatic material retaining an individuality. The chromosomes 
cannot be followed through these stages (not truly "resting stages”, 
the nuclei are evidently very active) when the chromatin has largely 
disappeared or is unstainable, and a nuclear reticulum has formed. 
One of the main points upon which the hypothesis of the individuality 
of the chromosomes rests receives no Support from Cumingia. Indeed 
the evidence here, as in the majority of cases reported, is against 
the hypothesis. The cell of Ascaris as described by Boveri (’09) 
still remains an isolated case in this respect. And even here one 
may justly have his doubts in spite of the renewed study of Boxne- 
viE (’08) of this cell, and her attempt to extend the hypothesis to 
include Allium and Amphiuma. 0. Hertwig’s position, consistently 
held since 1890, that it is impossible to follow an individual chro- 
mosome (idiochromosomes of course now excepted) through the resting 
stage of the nucleus, still seems best supported by cytological facts. 
The results of Moexkhaus (’04) obtained by Crossing Fundulus 
with Menidia are at present unique and furnish the best Support of 
this theory to the extent that it demonstrates some sort of a genetic 
continuity of the chromosomes; as does also the work of Bonxevie. 
