AND THE LOWER ANIMALS. 105 



occurred which, destroyed the whole brood. I had 

 seen enough, however ; and I believe I may say, that 

 from the publication of my researches and of M. de 

 BlainviUVs report, the metamorphosis of mollusks be- 

 came an established fact.* Other investigations have 

 since been made. From an examination of all these 

 works, we are justified in concluding that metamorpho- 

 sis occurs, in the entire group as well as in the classes 

 it comprises, and that it is in some instances complete, 

 in others incomplete, and occasionally entirely absent. 

 Of all classes of mollusks, the most fully investigated 

 from a development point of view is that of gastro- 

 pods, including such animals as the snail and slug. Both 

 these are air-breathing mollusks, and simply oviparous ; 

 and those which inhabit fresh water bring forth their 

 young in a somewhat similar manner. f Marine species, 

 on the other hand, undergo true metamorphoses. Let 

 us see, for example, what takes place in one of those 

 jphleb enter ate mollusks which have subjected me to so 

 many severe controversial attacks. J These animals 



* This report was read before the French Academy in 1835, and 

 had been prepared by a commission, consisting of Messrs. Geoffroy 

 Saint-Hilaire, F. Cuvier, and De Blainville. Perhaps the reader 

 may imagine that I allude too frequently to my own researches, but 

 I trust he will appreciate and excuse the feeling by which I am 

 actuated in thus referring to my earliest contribution to science. 



t Neritina fluviatilis is an exception ; the larvse of this mollusk 

 are exceedingly like those described and figured in M. Ed. Cla- 

 parede's beautiful work " Anatomie und Entwickelungsgeschichte 

 der fluviatilis Neritina." — Miiller's Archives, 1857. 



J When first I published my researches on phlebenterate mol- 

 lusks, and asserted that these animals have no distinct veins, I was 

 opposed by nearly every naturalist who had paid attention to the 

 subject. I think I may safely say that at present it is just the 



