270 WILBUR WILLIS SWINGLE 
The resting nucleus is not, therefore, a single structure any more 
than is the equatorial plate. It is composed of units, each of which, 
so far as known, has the properties of the entire nucleus, and the union 
of these vesicles into a single one may be considered as a secondary 
character. It is altogether probable that the chromosomes, and hence 
the chromosomal vesicles preserve their identity throughout the resting 
period, and I venture the suggestion that the daughter chromosomes 
will be found to arise within the chromosomal vesicles. 
The description just quoted, of the formation and behavior of 
chromosomal vesicles in gasteropod molluscs, applies equally as 
well to the conditions in the bullfrog larva, and certainly cannot 
be better stated than Professor Conklin's description (figs. 1, 2, 
3). 
Hacker ('95) reported that the chromosomes of the early cleav- 
ages of Cyclops brevicornis formed two groups of vesicles, one 
group from the paternal, the other from the maternal pronuclei. 
More recently, Wenrich ('16) has reported that each chroma- 
some in Phrynotettix becomes surrounded, as early as the ana- 
phase, by a hyaline region; that this region expands in the 
telophase; that the chromatin of each chromosome becomes 
diffused within its own region; that a membrane becomes formed 
at the boundary between the hyaline region and the cytoplasm, 
producing the chromosomal vesicle. The nuclear membrane 
consists of the outer walls of the vesicles at the periphery of the 
nuclear group. Wenrich concludes that the hyaline region is 
formed at the expense of the cytoplasm and that the material 
of each chromosome tends to remain within the space of its own 
vesicle, a core of chromatin being particularly noticeable in the 
center of this region, and that the prophase chromosome subse- 
quently formed, is developed out of the substance of one, and 
only one, of the previously existing telophase chromosomes. 
Conditions in Rana catesbeiana larvae, while not so clearly 
marked, in regard to individual chromosome vesicles, as those 
described for Orthopteran material, nevertheless strongly indi- 
cate that the 'polymorphic' nucleus of amphibians is nothing 
other than a group of large chromosomal vesicles, more or less 
independent, the outer walls of the outermost vesicles forming the 
nuclear membrane. 
