CELL AND ORGANISM 



103 



centrosome. These are reputed to be of aid 

 in the capture of prey. 



The possession by dinoflagellates of this 

 peculiar assemblage of organelles, namely, 

 nematocysts, tentacles, eyespots, is sugges- 

 tive of at least an analogy to the Coelen- 

 terata. The resemblance is heightened by 

 the fact that the tentacle in Noctiluca and 

 Erythropsis is at the side or end of the 

 mouth, and functions in the capture of food, 

 as do also the nematocysts. 



These examples bring us face to face with 

 the problem mentioned in the earlier part 

 of this paper, namely, the widespread ac- 

 ceptance of the embryonic method of evolu- 

 tion. In this view of evolution the multi- 

 cellular bodies of the Metazoa appear to 

 have evolved from the Protozoa by the 

 division of similar simple undifferentiated 

 cells to form morula, blastula, and gastrula 

 and later to become differentiated by cellu- 

 lar specialization in structure and function. 



In the light of the differentiations evolved 

 among Protozoa, and their tendency to be- 

 come multicellular, it seems to the speaker 

 that another method than the embryonic 

 was the one followed in reality ; namely, evo- 

 lution from Protozoa to sponges and coelen- 

 terates by multiplication of nuclei in an 

 already differentiated cytoplasm. In this 

 ease development of the individual by the 

 embryonic route was secondarily acquired 

 and only tends to obscure the actual mode 

 of evolution of these two metazoan phyla 

 from the Protozoa. 



To be specific, Polykrikos has indiffer- 

 ently 2, 4, or 8 cells. Its common mouth 

 and stock of nettling cells are used as the 

 organism has need. Its near relatives have 

 at least one tentacle per cell and some of 

 them add one eyespot. By a combination 

 in one organism of all of these organelles 

 with the tendency to multiplication of 

 nuclei, we arrive rather near to a primi- 

 tive coelenterate. 



A similar suggestive relationship exists 

 between the craspedomonad flagellates and 

 the Porif era. The Craspedomonadina form 

 colonies of both dendritic and tabular form. 

 The typical collar is not a closed funnel as 

 figured, but in reality a coiled spiral formed 



by a short attached flagellum of the undu- 

 lating membrane type with a slight overlap 

 above the mouth. Recent investigations 

 have shown that the collared cells of sponges 

 have a similar structure. Flagellates re- 

 lated to the Craspedomonadina form skeletal 

 structures, some of calcareous (Coccolitho- 

 phoridae) material and some of siliceous 

 (Silicoflagellata), and some craspedomonads 

 live in a lorica of a material resembling 

 elastin. The flagellates set the stage for the 

 arrival of the sponges in the drama of evo- 

 lution. Most of us well remember that 

 Saville-Kent 's great work on the Infusoria 

 included the simpler sponges. 



The Protozoa have all the basic functions 

 of life to perform. They require organelles 

 for digestion, excretion, locomotion, sensa- 

 tion and transmission, as well as for the 

 capture of food and circulation of its di- 

 gested products, and the support and pro- 

 tection of the body. An extraordinary 

 variety of patterns of structure and adap- 

 tions in function has been evolved among 

 them. Throughout this great variety of 

 structural evolution of cytoplasmic prod- 

 ucts the number of nuclei present in the 

 organism does not seem to play any con- 

 spicuous part. Polykrikos and some other 

 multicellular forms seem to thrive equally 

 well with different numbers of nuclei. A 

 conspicuous example of this indifference to 

 the number of nuclei is seen in the little 

 volvocid colonial flagellate, Platydorina. It 

 is formed by a blastula-like ellipsoid of one 

 layer of cells which flattens with interpola- 

 tion of the cells of the two faces in a spirally 

 twisted plate of 16 or 32 cells with 3 or 5 

 posteriorly directed tails. It swims equally 

 well with either number in a spiral course 

 by coordination of the flagellar strokes of 

 the cells of the organism. A parasitic in- 

 fection sometimes breaks out in the organ- 

 ism and various individual cells are de- 

 stroyed, but no matter which cells are de- 

 stroyed the swimming continues in the same 

 pattern. Organisms with only a single cell 

 still continue to rotate, feebly to be sure, 

 for the motive power is reduced, but the 

 pattern of behavior is still that of the 

 organism. 



