182 ESSAY ON CLASSIFICATION. Part I. 



of an as.sociation of the Rhizopods with the Algae.^ This would almost seem natural, 

 when we consider that the vesicles of many Fuci contain a viscid, filamentous 

 substance, so similar to that protruded from the body of the Rhizopods, that the 

 most careful microscopic examination does not disclose the slightest difference in its 

 structure from that which mainly forms the body of Rhizopods. The discovery 

 by Schultze^ of what he considers as the germinal granules of these beings, by no 

 means settles this question, though we have similar ovoid masses in Algoe, and 

 though, among the latter, locomotive forms are also very numerous. 



With reference to the Infusoria, I have long since expressed my conviction that 

 they are an unnatural combination of the most heterogeneous beings. A large 

 number of them, the Desmidiere and Volvocinse, are locomotive Algaa. Indeed, 

 recent investigations seem to have established beyond all question, the fact, that 

 all the Infusoria Anentera of Ehrenberg are Algte. The Enterodela, however, are 

 true animals, but belong to two very distinct types, for the Vorticellidae differ 

 entirely from all others. Indeed, they are, in my opinion, the only independent 

 animals of that group, and so fiir from having any natural affinity with the other 

 Enterodela, I do not doubt that their true place is by the side of Bryozoa, 

 among Mollusks, as I shall attempt to show presently. Isolated observations which 

 I have been able to make upon Paramecium, Ojialina, and the like, seem to me 

 sufficient to justify the assumption that they disclose the true nature of the 

 bulk of this group. I have seen, for instance, a Planaria lay eggs out of which 

 Paramecium were born, which underwent all the changes these animals are known to 

 undergo up to the time of their contraction into a chrysahs state ; while the Opalina 

 is hatched from Distoma eggs, I shall publish the details of these observations 

 on another occasion. But if it can be shown that two such types as Paramecium 

 and Opalina are the progeny of Worms, it seems to me to follow, that all the 

 Enterodela, with the exception of the Vorticellidaj, must be considered as the 

 embryonic condition of that host of Worms, both parasitic and free, the meta- 

 morphosis of which is still unstudied. In this connection, I might further remark, 

 that the time is not long past when Cercaria was also considered as belonging 

 to the class of Infusoria, though at present no one doubts that it belongs to 

 the cycle of Distoma; and the only link in the metamorphosis of that genus which 

 was not known is now supplied, since, as I have stated above, the embryo which 

 is hatched from the egg laid by the perfect Distoma is found to be Opalina. 



All this leads to the conclusion, that a division of the animal kingdom to be 

 called Protozoa, differing from all other animals in producing no eggs, does not 

 exist in nature, and that the beings which have been referred to it have now 



1 Comp. Ch.ap. I., Sect. 18, p. 75. ^ Schultze, (M. S.,) Polythakmien, q. a.; p. 24. 



