ON THE GROUP PROTOZOA. 39 



be sufficient to show, what Burmeister, Dana, and Leydig, have proved in another way, 

 that Rotifera are genuine Crustacea, and not worms. The vegetable character of most 

 of the Anentera has been satisfactorily illustrated. I have not yet been able to arrive 

 at a definite result respecting the Rhizopods, though they may represent, in the type of 

 Mollusks, the stage of yoke-segmentation of Gasteropoda. From these remarks it should 

 be inferred that I do not consider the Protozoa as a distinct branch of the animal king- 

 dom, nor the Infusoria as a natural class." 



" With reference to the Protozoa, first, it must be acknowledged that, notwithstand- 

 ing the extensive investigation of modern writers upon Infusoria and Rhizopoda, the 

 true nature of these beings is still very little known. The Rhizopoda have been wander- 

 ing from one end of the series of Invertebrata to the other, without finding a place gene- 

 rally acknowledged as expressing their true affinities. The attempt to separate them 

 from all the classes with Avhich they have been so long associated, and to place them 

 with the Infusoria in one distinct branch, appears to me as mistaken as any of the 

 former arrangements; for I do not consider that their animal nature is yet proved 

 beyond a doubt, though I have myself once suggested the possibility of a definite rela- 

 tion between them and the lowest Gasteropods.* Since it has been satisfactorily ascer- 

 tained that the Corallines and Nullipores are genuine Algre, which contain more or less 

 lime in their structure, and since there is hardly any group among the lower animals and 

 lower plants which does not contain simple locomotive individuals, as well as compound 

 communities, either free or adhering to the soil, I do not see that the facts known at 

 present preclude the possibility of an association of the Rhizopods with the Algre. This 

 would almost seem natural, when we consider that the vesicles of many Fuci contain a 

 viscid, filamentous substance, so similar to that produced from the body of the Rhizo- 

 pods, that the most careful microscopic examination does not disclose the slightest diffe- 

 rence 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, since we have similar ovoid masses in Algae, and since among the 

 latter locomotive forms are also very numerous." In a note it is added, that " the recent 

 investigations of Ehrenberg and J. Miiller indicate a very close affinity between the 

 Thalassicolae, the Polycystinre, and the Rhizopods ; and the more I examine these 

 enigmatical bodies, the more do they impress me as being allied to the lower Algae and 

 to the Sponges, rather than to any type of the animal kingdom." 



" 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 Desmidiacaa and Volvocinas — are locomotive Algae. Indeed, recent investi- 

 gations seem to have established beyond all question the fact, that all the Infusoria 

 Anenterata of Ehrenberg are Algae. The Enterodela, however, are true animals, but 

 belong to two very distinct types ; for the Vortieellidae differ entirely from all others. 

 Indeed, they are. in my opinion, the only independent animals of that group ; and, so 

 far from having any natural affinity with the other Enterodela, I do not doubt that 

 their true place is by the side of the Bryozoa, among the Mollusks, as I shall attempt 

 to show presently. Isolated observations, which I have been able to make upon Para- 

 mecium, Opalina, 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 



* Allusion is here made by Prof. Agassiz to the following passage, which occurs in a 

 Paper on the Principles and Classification of the Animal Kingdom, published in the 

 " Proceedings of the American Association for the Advancement of Science," Charleston, 

 March, 1850 : — 



"Again, the position of the Foraminifera seems to me no longer doubtful. They are 

 neither microscopic Cephalopoda nor Polype, as of late it has been generally thought best 

 to consider them, but constitute a truly embryonic type in the great division of Gastero- 

 poda, exemplifying, in the natural division, in a permanent condition, the embryonic 

 state of development of common Gasteropoda, during which the bulk of the yolk passes 

 through the process of repeated divisions." 



