Some ÖObservations on the Chromosome Vesieles in the Maturation ete. 91 
creased in size and reveals a sharp differentiation into two sub- 
stances, basichromatin and oxychromatin (see CONKLIN, 02, p. 9), the 
former becomes the chromosomes, the latter spindle rays, sphere 
substance and cytoplasm. 
No evidence of a chromosome vesicle was found in these early 
stages; each chromosome forms from a single small particle that 
increases in volume as maturation continues. In fig. 3, these bodies 
are more distinet and associated with the spindle fibres. The net- 
work of linin and oxychromatin substance is less and there is a 
corresponding increase in the number of the spindle rays. The next 
stage represented (Fig. 4), shows the chromosomes approximately 
full sized and in the region of the equator of the spindle. 
In all three species the chromosomes in the metaphase assume 
a variety of shapes (Fig.5). This irregular condition gives way to 
a simple rod-like chromosome which appears to,divide transversely 
in this and the second maturation spindle. ConKkLın (02) believes 
that the irregularity may be caused by the fact that the chromosome 
vesicles eonfine the chromatin to certain regions. He finds in Üre- 
pidula chromosome vesicles (Plate I, Fig. 12a) at this stage. I have 
not been able to detect in these three species of Nudibranchs similar 
structures. In discussing the irregularities in the form of the chro- 
mosomes he says (pp. 11—12): »It is diffieult to say whether these 
differences in the shapes of chromosomes mean much or not. On 
the one hand it is possible that all the chromosomes of a given 
mitosis cannot be reduced to a single type; that their differences in 
shape indicate differences in material substance, and that different 
chromosomes may therefore represent different heritable qualities. 
On the other hand these differences in the shapes of the chromosomes 
are generally limited to the first maturation division; they are rarely 
found in the second maturation and only to a limited extent in 
cleavage. Furthermore, there are many evidences that the shapes 
of chromosomes are conditioned by their linin sheaths, and that the 
chromatie substance which fills the sheath is of a semi-fluid or viseid 
character.« My observations on the early maturation stages in the 
Haminea may throw some light on the suggestion quoted. In this 
molluse the chromosomes assume an irregular form while in the 
chromosome vesicles; and further, they are irregular on the free sur- 
face and much smoother on the side or parts in contact with the 
linin sheath. In this speeies the chramosomes do not fill the linin 
sheath in the prophase stage which affords an apportunity to note 
