Organisms Consisting of One Cell 237 



the reason for tlie cliolce of this name: "Some species arv 

 among the most admirahle forms of Radiohiria, and are sinii- 

 Lar to small elegant Medusae, The form of the shell ex- 

 hibits the same varieties as the similar umbrella of tlie 

 Medusa. . . . The similarity witli the umbrella of a Me- 

 dusa is so great, that In many species the large lower open- 

 ing on the moutli of the shell is surrounded by a pronjinent 

 ring or diaphragm, comparable to the velum of the Cras]^>e- 

 dotae or Hydromedusae." ^ This general resemblance to 

 certain medusae Is made still more striking in such a s})ecies 

 as GazeUetta crijtonema by the phaeodium, a mass of cell- 

 like pigment-bearing structures "in the lower half of the 

 shell cavity," ^ sometimes, as in the figure referred to, pro- 

 truding from the mouth of the shell. No one can compare 

 this figure with those of various medusae which liear gonads 

 or buds on the manubrium or the subumbrellar region with- 

 out being struck by the general resemblance between Hiem. 

 The reader must not infer from this comparison that the 

 points of resemblance signify anything like close corre- 

 spondence in structure. As a matter of fact the two ani- 

 mals are no more alike than a bat and a butterfly. The 

 sole point of significance, so far at least as this discussion 

 is concerned, is that judged by the facts of actual structure 

 and function of the radlolarian and the coelenterate, the 

 first is hardly if at all more simi)le than the second — is not 

 a whit less a true animal. 



(c) Comparison of the Shell of a Hhizopod and of (t SantUus 



One more comparison between a "simple" unicellular ani- 

 mal and a complex multicellular "true" animal is as far as 

 we can go in the strictly com])arative-anatomy ])art of this 

 presentation. Take, for example, the shell of () /nrciiUna, 

 the detailed structure of which was worked out by W. B. 

 Carpenter. Some of the schematic figures in his work are 



