EMBRYOLOGY OF CRYPTOBRANCHUS ALLEGHENIENSIS. l6l 



Two days after the egg is laid, cell division in the upper 

 hemisphere has advanced until the individual cells can no longer 

 be seen with the naked eye. The macromeres are in general 

 still quite large, but in several instances there was noted a greater 

 multiplication of cells about the lower pole than in the equatorial 

 region (see Fig. 24^). 



F. Comparison icifh OtJicr Forms. De B ussy ('05) has de- 

 scribed the principal segmentation stages of the eggs of C. 

 japonicus. His material lacked eggs in the 2- cell and 4-cell 

 condition ; but beginning with the 8-cell stage the later cleavage 

 stages are described and illustrated. A comparison with my 

 own sketches of the segmentation of the eggs of Cryptobranckus 

 allegkeniensis, made before I knew of the existence of de Bussy's 

 paper on C. japonicits, shows, as might be expected from the 

 close relationship of the two forms, a marked similarity in the mode 

 of cleavage. Since de Bussy's paper includes a comparison of the 

 eggs of C.japonicns with those of other forms, a similar discussion 

 for C. allegheniensis at the present time seems unnecessary. It 

 should be added, however, that the segmentation of the eggs of 

 Desmognathus, described by Wilder ('04) and Hilton ('04) also 

 bears a considerable resemblance to that of Cryptobranchus. 



I take pleasure in acknowledging my indebtedness for encour- 

 agement and advice to Prof. Jacob Reighard, at whose sugges- 

 tion I first looked for the eggs of Cryptobranchus, and to Dr. O. 

 C. Glaser, under whose direction the work was carried on after 

 I returned to the university. 



ZOOLOGICAL LABORATORY, UNIVERSITY OF MICHIGAN, 

 ANN ARBOR, MICHIGAN. 



