278 BERTRAM G. SMITH. 



EXPLANATION OF PLATE V. 



Cryptobranchiis allegheniensis. 



FIGS. 21 AND 22. Two successive meridional sections through a single nucleus 

 preparing for the second cleavage mitosis. The sections extend at right angles 

 to the first cleavage furrow, and close to the other cleavage-nucleus. A consider- 

 able part of the nucleus here shown is left in an adjacent section where it is not so 

 clearly separated into two nuclear vesicles. Fixed in bichromate-acetic-formalin; 

 stained with borax-carmine Lyons-blue picric-acid. X 400. 



FIG. 23. Horizontal section through a single nucleus preparing for the second 

 cleavage mitosis; the nucleus is almost entirely confined to this section. The first 

 cleavage furrow extends in a direction nearly parallel to a line connecting the two 

 asters. Bichromate-acetic-formalin fixation; stained with borax-carmine Lyons- 

 blue picric-acid. X 400. 



FIGS. 24, 25 AND 26. Three successive horizontal sections through a single 

 nucleus entering upon the second cleavage mitosis; all but a very small portion of 

 the nucleus is included in these sections. The first cleavage furrow extends in a 

 direction nearly parallel to a line connecting the two asters. Bichromate-acetic- 

 formalin fixation; stained with borax-carmine Lyons-blue picric-acid. X 400. 



