AND THE LOWEK ANIMALS. 167 



his plan, just making a few trivial alterations/* and 

 shall regard each one of the foregoing examples as 

 characterizing, by the nature and succession of its 

 developmental phases, one of these five groups. In 

 the first section we shall place the Hydra, and all 

 animals, no matter what their position in the zooiogic 

 scale, which propagate in a similar manner; in the 

 second we shall rank the compound Ascidians ; in the 

 third the Aphides ; in the fourth the Biphorae ; and 

 in the fifth the Aurelia. 



It is necessary, too, that in each of these sections, 

 the process of geneagenesis shall always take place 

 identically. In proportion as we obtain an accurate 

 knowledge of these strange phenomena, we observe 

 that each phase of development is in almost every species 

 accompanied by different and occasionally quite un- 

 expected peculiarities. Since it would be impossible 

 here to describe all the facts in connection with this 

 subject, we shall limit ourselves to a resume of the 

 more curious ones which are presented to us by the 

 principal groups of the animal kingdom ; and we shall 

 follow the zoological scheme, without confining our- 

 selves closely to Yan Beneden's classification. In 

 taking this course we shall only be acting consistently 

 with the plan pursued in other portions of this volume. 

 Besides, we shall by this means expose a result of 

 much importance ; we shall show how the phenomena 

 become progressively more complex in proportion as 



* In the work in which he proposes these divisions, " La Gene- 

 ration alternante et la Digenese," Van Beneden places under the 

 third section animals which in my opinion belong to the second. 

 He places the aphides last, although their geneagenesis is far more 

 simple than that of either the Medusae or the intestinal worms. 



