174 THE RELATION OF THE TYPICAL FORM 



contractile bodies, the so-called contractile vesicles, and a diffuse 

 digestive system. Perhaps now you may call to mind some of 

 the Protozoa for instance this animal, (fig. 25, p. 51,) a Podoph- 

 rya, which, as it appears at this stage of growth, is an appar- 

 ently symmetrical, four-sided, inverted pyramid in which you 

 cannot discover any signs of that obliquity of which so much 

 has been said ; and you will be induced therefore to set them 

 down as exceptions to the rule. Now this apparent discrepancy 

 has been one of the stumbling-blocks of naturalists, and has 

 thrown some of them at least off the true course of develop- 

 ment; and like the stragglers of a grand army, although they 

 follow mainly in its line of march, they scatter about here and 

 there, picking up anything and everything they can get hold of.* 

 Now as I do not wish to anticipate anything, I will defer the 

 removal of this stumbling-block until another occasion. 



My present aim is simply to explain the relation of the type 



* See the sensational assertions of L. Agassiz in regard to the systematic posi- 

 tion of various Protozoa; for instance, in the " Proceedings of the Boston Society 

 of Natural History," vol. in. Nov. 6, 1850, p. 354, he declares that the well- 

 known parasites (Trichodina) of Hydra are Medusae. " In the eggs of Hydra, 

 he had been able to trace all the forms from a segmented yolk to these parasites ; 

 the fresh-water Hydra is the Polypoid form of Medusas, while these parasites are 

 the Medusoid form." Of the same degree of reliability is his assertion in his 

 " Essay on Classification," Boston, 1857, p. 182, or the London edition, 1859, 

 p. 291, where he says, "I have seen, for instance, a Planaria lay eggs out of 

 which Paramecium was born, which underwent all the changes these animals are 

 known to undergo up to the time of their contraction into a chrysalis state ; 

 while the Opalina is hatched from Distoma eggs." Or " Essay," &c., p. 75 ; 

 Lond. ed. p. 112: " Having satisfied myself that Colpoda and Paramecium are 

 the brood of Planariae." Finally, to complete the disjointure of this homogeneous 

 group, and its entanglement with Articulata through Opalina, and with Medusae 

 through Trichodina, he asserts, in another part of that same essay, that the Vorti- 

 cellidas, which were well known, long before the time he wrote, to be the crown- 

 ing rahk of Protozoa, "differ entirely from all others," (p. 182; Lond. ed. 

 p. 290,) i. e., such as Stentor, Paramecium, and the rest of the Enterodela, and 

 that he had satisfied himself of the "propriety of uniting the Vorticellidfe with 

 Bryozoa," (p. 72 ; Lond. ed. p. 108). While I am about it, I would venture to 

 guess that that author's pretended Hydroid animals of Millepora are mere para- 

 sites ! 



