GERM CELLS OF ANUBANS 269 
2. The polymorphic nuclei of amphibians 
Practically all investigators of the germ cells of urodeles and 
anurans have described and figured the bizarre and striking 
lobulation' of the spermatogonial nuclei of these forms, but few 
have attempted any explanation of the pecuharity. Most of 
the earUer investigators regarded the nuclear polymorphism as 
stages in amitotic division. The writer has observed, however, 
that the striking nuclear lobulations of the spermatogonial nuclei 
in Rana catesbeiana larvae, are nothing more or less than chromo- 
somal vesicles and fusions of such vesicles. In reality, the poly- 
morphism of nuclear structure is due to these vesicles, remaining 
more or less distinct and independent froni one another. That 
this view is essentially correct is readily seen by examination of 
early prophase and late telophase spermatogonial divisions. In 
early prophases the individual chromosomes arise by condensa- 
tion of the chromatin material of the vesicles. Later telophases 
clearly show the formation of the vesicles which increase greatly 
in size as the cell grows. 
ConkHn ('02) has called attention to the occurrence of such 
chromosomal vesicles in Crepidula. He states in this regard: 
1. The chromosomes, consisting of chromatin enclosed in a linin 
sheath, divide and move to the poles of the spindle, where they par- 
tially surround the spheres. 2. Here they become vesicular, the 
interior of the vesicle becoming achromatic, though frequently contain- 
ing a nucleolus-Iike bod}^, while the wall remains chromatic. 3. These 
vesicles continue to enlarge and then unite into the 'resting' nucleus. 
The nuclear membrane is composed of the outermost walls of the 
vesicles, while the inner walls stretch through the nucleus as achromatic 
partitions. 
Again on page 47 of his ('02) communication, Conkhn writes: 
It sometimes happens, especially in eggs in which more than the 
normal number of centrosomes and asters are present, that some or all 
of the chromosomal vesicles do not fuse, but remain distinct through 
the whole of the resting period. In such cases each of the vesicles 
behaves like a miniature nucleus, absorbing achromatic material and 
forming a net-work of chromatin either within the vesicle or on its 
walls. In this growth and differentiation the vesicles keep pace, step 
by step with the normal nucleus, so that one must regard the resting 
nucleus as virtually composed of vesicles, though their union may be 
so intimate as to hide this structure. 
