222 



THE AMERICAN NATURALIST. [Vol. XXXVIII. 



changes have taken place the macromere which is designated 

 by the letter D divides independently of the three other macro- 

 meres into two cells of unequal size but both containing yolk 

 spheres. The smaller cell is concerned in giving rise to the 

 mesoblastic bands and is entirely covered above by the micro- 

 It can be seen from the brief description ot the carlv segmen- 

 tation stages and the accompanying sketches that Haviiuca so/i- 

 taria does not exhibit any segmentation phenomena other than 

 those characteristic of mollusca. Ihe subsequent cleavage 



i have been followed sufficientlv to indicate that they are 

 reement with related forms that have been described 



egins to move in the egg capsule at the 



le embryo usually be 



of the seventh day ; the cilia on the mantle borde 

 rcntiatccl ant! can be seen in motion. It is difficult to 

 rtain the e\aa length ol time the embrvo remains in the 

 ^■ai.sulc hut I ha\c known it to continue there for a week. 

 i"st ..t the misses that hi\c been undei obser\ation the 

 yos Ikivc died betoie becoming fice suimmm^ mdiMduds 

 >ugh sdtne weie immediatelv placed m aciuaria or in the 



