ALTERNATE AND EQUIVOCAL REPRODUCTION. 165 



Infusoria, passes in succession through all the phases we 

 have described. But the remarkable point in these meta- 

 morphoses is, that what was at first a single individual is 

 thus transformed, by transverse division, into a number of 

 entirely distinct animals, which is not the case in ordinary 

 metamorphoses. Moreover, the upper segment does not 

 follow the others in their development. Its office seems to 

 be accomplished so soon as the other segments begin to be 

 independent, being intended merely to favor their develop- 

 ment, by securing and preparing the substances necessary 

 to their growth. In this respect, it resembles the nurse of 

 the Cercaria. 



348. The Hydroid Polyps present phenomena no less 

 numerous and strange. The Campanularia has a branching, 

 plant-like form, with little cup-shaped cells on the ends and in 

 the axils of the branches, each of which contains a little 

 animal. These cups have not all the same 

 organization. Those at the extremity of 

 the branches, (,) and which appear first, 

 are furnished with long tentacles, where- 

 with they seize their food, (Fig. 143.) 

 Those in the axils of the branches, and 

 which appear late, are females, (,) and 

 have no such tentacles. Inside of the lat- 

 ter, little spherical bodies are found, each 

 having several spots in the middle ; these 

 are the eggs. Finally, there is a third 

 form, different from the two preceding, 

 produced by budding from the female polyp, to which it in 

 some sort belongs, (c.) It is within this that the eggs ar- 

 rive, after having remained some time within the female. 

 Their office seems to be to complete the incubation, for it is 

 always within them that the eggs are hatched. 



349. The little animal, on becoming free, has not the 



