104 



THE CELL AND PROTOPLASM 



In view of this indifference of the proto- 

 zoan organism to the number of nuclei and 

 to the fact that increase in the number of 

 nuclei in the Protozoa, except in the matter 

 of sex and somatic cells, does not seem to 

 be the basis for the remarkable differentia- 

 tions evolved in the protistan organism, we 

 may infer that the path of structural and 

 functional evolution of primitive organisms 

 has been in the cytoplasm. The relation of 

 genes to this process is not different in prin- 

 ciple in the Protozoa and Metazoa. The 

 cytoplasmic differentiations in the absence 

 of sexual reproduction are transmitted, at 

 fission, with restoration of the missing half 

 as in the skeleton of the dinoflagellates, in 

 other flagellates and in ciliates with more 

 evidence of dedifferentiation and redifferen- 

 tiation. There is therefore in these primi- 

 tive organisms an inheritance of the ac- 

 quired cytoplasmic structures. 



The transition from these primitive, pre- 

 sumably haploid organisms, to the diploid 

 with the emergence of sexual reproduction 

 seems to have occurred in the higher types 

 in the different classes of Protozoa quite 

 independently of one another. What ap- 

 pear to be encysted zygotes have been found 

 in a very few marine and in one fresh-water 

 dinoflagellate ; and sexual reproduction in 

 the classic form is definitely known to occur 

 in the Volvocidae. It is also definitely 

 proved to occur in the Foraminifera, but 

 remains to be proved in the Radiolaria, 

 while it seems to be universal in Sporozoa 

 and Ciliata. Sexual reproduction is, at 

 least as far as is yet known, wholly absent 

 in the more primitive Sarcodina and Flagel- 

 lata. Since both the Porifera and the Coel- 

 enterata reproduce sexually, it is presum- 

 able that they evolved from types of Flagel- 

 lata in which sexual reproduction had 

 already arrived. 



Reverting again to the problem of the re- 

 lation of the Protozoa to the Metazoa and 

 to the method by which the latter evolved 

 from the former, we find two points of view 

 as to the method. According to the widely 

 prevalent view, the metazoan is formed as 

 a colony of unicellular Protozoa which later 

 differentiate as do the cells of the metazoan 



embryo which in so doing repeat the ances- 

 tral history. Underlying this point of view 

 is the old concept of the wall of the cell as 

 an essential part and of structural separate- 

 ness of the cytoplasm associated with each 

 of the several nuclei, and still more basic is 

 the underlying philosophy that the cell is 

 the determining factor in the living body 

 and not that body itself, the organism as a 

 whole. 



The second point of view regards the 

 organism as a whole as the determining fac- 

 tor and the individual cells as its product. 

 The organism is a living pattern of cellular 

 units, self-regulating and self-maintaining. 

 Cell boundaries are not an essential part 

 of the concept of the cell, although this idea 

 has the rigidity and persistence of masonry 

 wall. So long as the nucleus has a domain 

 of cytoplasm for interaction the construc- 

 tive activities continue. It is quite con- 

 ceivable that limits of such interaction may 

 shift, overlap, contend with neighboring 

 nuclei, and wax and wane with the impact 

 of external factors. The essential feature 

 of the individuality of the cell is not its 

 boundary, but a functioning set-up of 

 nucleus and cytoplasm. 



The temporary independence of each 

 from the other is experimentally proved, 

 at least for the cytoplasm. Enucleated cells 

 continue to live and move as masses of pro- 

 toplasm capable of katabolic metabolism 

 but soon wear out. They do not form a new 

 nucleus. In fresh preparations of mucus 

 from the intestine of the frog, I have seen 

 Trichomonas, full of activity and ceaselessly 

 moving, with the nucleus with attached 

 neuromotor fibrillar structures consisting of 

 blepharoplast, axostyle, undulating mem- 

 brane and the full complement of flagella, 

 and with no visible shred of undifferen- 

 tiated cytoplasm attached thereto. This 

 species has the habit of dropping off bits of 

 cytoplasm from the posterior end of the 

 axostyle. In the instances observed, this 

 process had stripped the organism of all 

 cytoplasm except that part differentiated 

 into permanent structures and structurally 

 adherent to the nuclear membrane. This is 

 not, of course, strictly an isolated nucleus. 



