Organisms Consisting of One Cell 237 



the reason for the clioice of this name : "Some species are 

 among" the most admirable forms of Radiolaria, and are simi- 

 hir to small elegant Medusae. The fonn of the shell ex- 

 hibits the same varieties as the similar umbrella of the 

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

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

 ing on the mouth of the shell Is surrounded by a prominent 

 ring or diaphragm, comparable to the velum of the Craspe- 

 dotae or Hydromedusae." * This general resemblance to 

 certain medusae is made still more striking in such a species 

 as Gazelletta crytonema bj 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. Xo one can compare 

 this figure with those of various medusae which bear gonads 

 or buds on the manubrium or the subumbrellar region with- 

 out being struck by the general resemblance between them. 

 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 radiolarian and the coelenterate, the 

 first is hardly if at all more simple than the second — is not 

 a whit less a true animal. 



{c) Comparison of the Shell of a Rhizopod and of a Xaatilus 



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 comparative-anatomy part of this 

 presentation. Take, for example, the shell of Operculina, 

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

 Carpenter. Some of the schematic figures in his work are 



