GERMAN VERSION. 3 



manner on a common polypidom and form a loliole, or 

 colony wliicli, as regards tlie welfare of the species, stands 

 in the same relation to it, that the hive of bees with its 

 colony of three differently-formed broods of young, does 

 to the bee species. It naturally follows that mention 

 should here be made of the mode of propagation of the 

 Balpcs (Chap. Ill), (although indeed the observation of 

 the worthy Chamisso has been otherwise interpreted, but 

 in a way of which science has not availed herself, how- 

 ever plausible the interpretation may have appeared to 

 the superficial reader ;) and thus we have an alternation of 

 generations, exhibited to us in the molluscous class, and 

 it is certainly not confined to the Salpce only, but extends 

 to all the compound Ascidians {Ascidia compositce). In 

 the class Entozoa my researches have sufficed to prove 

 not only the existence of such an " alternation of Gene- 

 rations," but to show besides, that traces of a similar 

 mode of development are visible in almost all the divi- 

 sions of that class. According to recent observations it 

 is, however, exhibited most clearly in the IVematoda 

 (Chap. IV), in which I prove that the CercaricB are the 

 larva of JDistomata, and that they become true pup(S ; 

 that the animals in which the Cercarice originate and 

 grow up are peculiar trematode individuals, descended in 

 the second or third generations from Distomata, and 

 consequently not produced directly from their ova, but 

 which, however anomalous they may at first sight appear, 

 constitute a precedent generation having for its object 

 the perfecting of the subsequent one. 



To similar observations belong also the description 

 given long ago by Ehrenberg of the cyclical development 

 of the Vorticella, and the already long-known though 

 misunderstood mode of propagation which obtains in the 

 Aphides. 



The existence of an alternation of generations having 

 in this way been established, not generally only, but even 

 as it seems in all the lower classes, beyond doubt, it is 



