IOWA ACADEMY OF SCIENCES. 33 



another process takes place, two individuals becoming adher- 

 ent, the cell walls in the region of contact being dissolved as 

 punctured, and an interchange of the protoplasm taking place. 

 After this the individuals separate and the process of fission is 

 renewed, and goes on for many generations. Ultimately, how- 

 ever, the process of conjugation is again resorted to. 



In certain of the Vorticellidce the reproductive process is still 

 further complicated by the fact that the fission is not simple 

 but multiple, one of the halves resulting from simple fission 

 again dividing into a number of small ciliated bodies, each of 

 which is capable of uniting with a normal vorticella iu the pro- 

 cess of conjugation. 



In certain Acinetans the multiple fission is internal, the 

 parent cell having its contents broken up into a number of 

 ciliated bodies, which escape through the ectosarc. 



We thus see that in going from the lower to the higher Pro- 

 tozoa we find the reproductive process growing more and more 

 complicated. First in the amoeba we find simple fission, then 

 in the Paramecium we find simple fission plus conjugation. In 

 the vorticella we have simple fission plus multiple fission plus 

 conjugation. In the acinetan we find simple fission plus inter- 

 nal multiple fission plus conjugation. 



Such, then, are the facts. We now turn to seek arr 

 explanation. 



Anabolism is the constructive, conservative, potential energy 

 of the cell. 



Katabolism is expressed in the destructive expenditure of 

 this energy in active or kinetic processes. 



The growth of any normal cell has a necessary limit due tO' 

 a purely physical cause. The mass increases as the cube of: 

 the diameter, while the surface increases only as the squarev 

 The surface performs the function of respiration, but it cannot 

 perform this function for an unlimited mass any more than a 

 cubic inch of lung can perform respiration for a full grown 

 man. 



As a cell increases in size its mass increases more rapidly 

 than its surface, until a point is reached beyond which it can 

 not grow, because the surface can supply no more oxygen. It 

 is worked to its limit, and can not respond to increased demands.. 

 At this stage there are three possibilities: 



First. — Death, which would end the question. 



Second. — Stationary balance, which is impossible. 



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