276 BERTRAM G. SMITH. 



EXPLANATION OF PLATE IV. 



Cryptobranchus allegheniensis. 



FIGS. 15 AND 1 6. Two successive horizontal sections showing a single nucleus 

 rotating into position for the second cleavage mitosis; almost the entire nucleus is 

 confined to these two sections. The newly-formed first cleavage furrow extends 

 in a direction parallel to a line connecting the two asters. Fixed in bichromate- 

 acetic-formalin; stained with iron-haematoxylin. X 400. 



FIG. 17. Horizontal section through a single nucleus in position for the second 

 cleavage mitosis; the greater part of the nucleus lies in this section. The newly- 

 formed first cleavage furrow extends in a direction parallel to a line connecting the 

 two asters. Fixed in Zenker's fluid; stained with iron-hsematoxylin. X 400. 



FIG. 1 8. Horizontal section through the other nucleus of the egg containing 

 the nucleus shown in Fig. 17. Orientation as in the preceding figure. Stained 

 with iron-hjematoxylin. X 400. 



FIG. 19. Horizontal section showing a single nucleus in position for the second 

 cleavage mitosis; the entire nucleus lies in this section. The newly-formed first 

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

 Bichromate-acetic-formalin fixation; stained with borax-carmine Lyons-blue picric- 

 acid. X 400. 



FIG. 20. Horizontal section through the other nucleus of the egg used for Fig. 

 19. A small part of one nuclear vesicle, and the greater part of the other, lies in an 

 adjacent section. Orientation as in the preceding figure. Stained with borax- 

 carmine Lyons-blue picric-acid. X 400. 



