286 BERTRAM G. SMITH. 



EXPLANATION OF PLATE IX. 

 Cryptobranchus allegheniensis. 



FIG. 45. Diagrams illustrating the orientation of the germ-nuclei during the 

 first four cleavage divisions. All the diagrams represent horizontal sections, and 

 the germ-nuclei are assumed to lie always in the same horizontal plane. The size 

 of the nucleus is exaggerated in proportion to the size of the egg. Dotted lines 

 represent beginning cleavage furrows; solid straight lines represent cleavage fur- 

 rows which have cut to the level of the nuclei. The number of chromosomes 

 formed from each germ-nucleus is assumed to be six, and this is probably the correct 

 number. 



A. Germ-nuclei and asters in position for the first cleavage mitosis. 



B. First cleavage mitosis. 



C. Newly-formed daughter-nuclei of the first cleavage mitosis. 



D. Nuclear vesicles and asters in position for the second cleavage mitoses. 



E. Second cleavage mitoses. 



F. Newly-formed daughter-nuclei of the second cleavage mitoses. 



G. Nuclear vesicles and asters in position for the third cleavage mitoses. 

 H. Third cleavage mitoses. 



I. Newly-formed daughter-nuclei of the third cleavage mitoses. 



J. Nuclear vesicles and asters in position for the fourth cleavage mitoses. 



K. Fourth cleavage mitoses. 



L. Newly-formed daughter-nuclei of the fourth cleavage mitoses. 



