310 EMBRYOLOGY AND CLASSIFICATION. 



the Gasteropods, described above. I have satis- 

 fied myself .of this fact while studying the trans- 

 formation of the young of our common Squid 

 (Loligo illecebrosa) . Nor are the young of our 

 common Bivalves, and even those of our Ascidians 

 (the so-called soft-shelled Clams) or of the Bryo- 

 zoa, essentially different ; while a closer compari- 

 son of the condition of the young of the two latter 

 groups, during the stage when they swarm in the 

 water as free floating animals, will readily show 

 that they bear a similar relation to the young 

 Gasteropods and the young Cephalopods as the 

 Echinoderm Iarva3 bear to the young swarming 

 Acalephs or the young Polyps. In the later 

 phases of their advance toward a mature con- 

 dition they constantly recall the appearance and 

 form of other representatives of their respective 

 classes, so that even an imperfect acquaintance 

 with this subject leads to the inference that there 

 probably exists between the successive stages of 

 growth of the Mollusk the same correspondence 

 with the different members of their respective 

 classes, in their natural gradation, as has already 

 been observed in the other types. A comparison 

 of the young of many Gasteropods, which, like 

 Natica, Pyrula, Buccinum, and Purpura, under- 

 go their early development in solid egg-cases, 

 has already furnished very interesting results ; 

 and collectors cannot be too careful in gather- 



