140 



BIOLOGICAL LECTURES. 



from the data thus afforded. There is, for example, no con- 

 clusive evidence of the inference that the bodies of all Metazoa 

 are to be considered as a connected mass, and not as a colony 

 of cells, because the cells of the bodies of the more complex 

 invertebrates and vertebrates have been found to have such 

 close protoplasmic connections that no cellular independence 

 of action is possible. The highly differentiated tissues of com- 

 plex structures which stand high in the gradations of any 

 genetic series might possess in every case examined the char- 

 acters that have been relied upon to disprove the cell theory, 

 and yet the simple primitive forms of the same genetic series 

 have less closely connected and more independent cells even 

 in their full-grown stages. 



Who knows, also, what the closer study of the ontogeny may 

 bring out with regard to the connections of cells, especially 

 in the building up of the earliest stages among the simplest 

 forms of each great group .-' There is, it appears to me, no 

 solid objection in embryology to the old theory of the rise of 

 the Metazoa out of Protozoa by a series of gradations that are 

 more or less distinctly traceable in the embryology of the 

 Metazoa, especially if the position taken by the lecturer is 

 true, that Volvox and Eudorina of the fresh waters is an inter- 

 mediate type, a real mesozoon, standing between the Protozoa 

 and Metazoa, and representing in their permanent aspect the 

 transient, single-layered blastula of the true Metazoa.^ 



Even leaving this out as inadmissible does not vitiate the 

 view taken by the advocates of the cell theory so far as the 

 obvious morphic phenomena are concerned. The evidence 

 that the earliest stages of the ovum in the most primitive 

 forms of the different classes of the animal kingdom, as a rule, 

 recapitulate the essential characters of the more primitive Pro- 

 tozoa, or, in other words, possess a reminiscent protozoanal, 

 unicellular stage, seems macroscopically and microscopically 

 demonstrated. In order to destroy the evidence of this obvi- 

 ous morphic basis, it would be necessary to prove that the ova 



1 " Larval Theory of the Cellular Tissue," Proc. Bost. Soc. Nat. Hist., vol. xxiii, 

 1884, p. 151. Also "Values in Classifications of Stages of Growth and Decline," 

 etc., Am. Nat., 18S8, p. S72. 



