138 REPRODUCTION. 



rate. Among the Aphides the number is much greater 

 still. 



356. The study of alternate generation, besides making 

 us better acquainted with the organization of animals, 

 greatly simplifies our nomenclature. Thus, in future, in- 

 stead of enumerating the Distoma and the Cercaria, or the 

 Strobila, the Ephyra and the Medusa, as belonging to 

 different classes and families, only the name originally given 

 to the perfect animal will be retained, and the rest be struck 

 from the pages of Zoology, as representing only the transi- 

 tory phases of the same species. 



357. Alternate generation always presupposes several 

 modes of reproduction, of which the primary is invariably by 

 ovulation. Thus, we have seen that the Polyps, the Medusa, 

 the Salpa, &c., produce eggs, which are generally hatched 

 within the mother. The subsequent generation, on the con- 

 trary, is produced in a different manner, as we have shown 

 in the preceding paragraphs ; as among the Medusse, by 

 transverse division ; among the Polyps and SalpaB, by 

 buds, &c. 



358. The subsequent generations are, moreover, not to 

 be regarded in the same light as those which first spring 

 directly from eggs. In fact, they are rather phases of de- 

 velopment, than generations properly so called ; they are 

 either without sex, or females whose sex is imperfectly de- 

 veloped. The nurses of the Distoma, the Medusa, and the 

 Campanularia, are barren, and have none of the attributes 

 of maternity, except that of watching over the development 

 of species, being themselves incapable of producing young. 



359. Another result of the above observations is this, that 

 the differences between animals which are produced by 

 alternate generation are less, the earlier the epoch at which 

 we examine them. No two animals can be more unlike, 

 than an adult Medusa (Fig. 31) and an adult Campanularia 



