46 PROCEEDINGS OF THE AMERICAN ACADEMY 



to be sure, myriads of such forms, and if, in the present state of 

 science, they can consistently be called by any name, I should prefer 

 that of Zooids, or animal-like forms. They appear to me to be inter- 

 mediate conditions of bodies, or a kind of stepping-stones, by means 

 of which some future true animal is to reach its perfect form. Modern 

 research in the class of Infusoria indicates that its component forms 

 are of this kind, and therefore that this whole class is likely to be 

 taken by the remaining classes of the Invertebrata, when more ex- 

 tended study shall, have made us more familiar with their details. 

 I would therefore insist that cell-processes, however closely inter- 

 woven they may be with the expressions of individual life, cannot be 

 considered as constituting the ground-work of its definition. True indi- 

 vidual animal life seems to involve a cycle of relations not implied in 

 simple cells ; in other words, these last must always lose their char- 

 acter as such, in a definite form which belongs to the individual. The 

 true generative act involves conditions which are peculiar and quite 

 distinct from any of the other physiological conditions of life ; it 

 must be regarded as resulting only from the conjugation of two op- 

 posite sexes, — a sexual process where the potential representatives 

 of two individuals are united for the evolution of one germ. The 

 germ-power thus produced may be extended and branched by bud- 

 ding, &c., but it can be formed only by the act of generation ; and the 

 multiplication of animals by the processes of fission or of germi- 

 nation is of no higher physiological character than the mere seg- 

 mentation of cells, or the reproduction of lost parts in the lower 

 animals." 



Professor Agassiz observed, that there was only an aiialogy 

 between the segmentation of simple cells and the segmentation 

 of the ovum, and went on to show the difference of the phe- 

 nomena presented in the two cases. 



As to the egg-like bunches, mentioned by Dr. Burnett as 

 found in the bodies of the Aphides, and considered by him as 

 " buds," and not as true " eggs," Professor Agassiz could not 

 agree with him. From the absence of peduncles, these free 

 cells had not the first characteristic of buds, and he was inclined 

 to consider them rather as true eggs. He mentioned the in- 

 stance of turtles, in which there are three kinds of eggs in 

 different stages of fecundation or growth, some to be laid this 



