200 TREADWELL. [VOL. I. 



meres of the fifth generation are given off. These differ from 

 other forms in the fact that the resulting micromeres a s , b\ c\ 

 d* are larger than the cells at the vegetative pole A s , B s , C s , D 5 . 

 Owing to lack of fresh material I have been unable to 

 follow the history of the cross furrow, but it is interesting to 



1,1.1 



FIG. 5. Seventy-cell stage from vegetative pole, showing bilateral division of </*. c 3 - 2 and d$- 2 

 have already divided. The other three members of the fourth quartette are beginning to 

 invaginate. 



note that in all specimens which I have seen it has the same 

 direction with respect to the cell x 1 ' 2 which it has in Podarke. 



I have been unable with the material at hand to discover the 

 formation of the mesoderm. 



Sthenolais picta. 



I have followed the segmentation of this annelid only as far 

 as the 64-cell stage, but in all respects it agrees exactly with 

 Podarke. The cross furrow takes and retains the typical 

 direction, and the cell x 1 ' 2 is formed at the same place and 

 time as in the other species. 



Hydroides diantJins. 



In this annelid the 32-cell stage is formed as in the other 

 cases, but beyond this stage important differences appear. The 



