170 



BIOLOGY: GENERAL AND MEDICAL 



Such cells may be given off at any time after the parent 

 attains to a certain development, after the completion 

 of which, the purpose of life having been fulfilled, it 

 usually becomes decadent. 



Among the most lowly living things, both animal and 

 vegetable, growth is regularly followed by fission or 

 budding. But as the higher organisms are reached, and 

 the foreshadowings of organs appear, multiplication 

 becomes complicated by conditions not clearly under- 

 stood, though no doubt of deep biological significance. 



FIG. 70. Volvox globator, showing the uniform and unspecialized character 

 of the cell structure. The large cells, o and s, the oocytes and spermatocytes, 

 are the reproductive cells and alone show specialization. (Lang.) 



Thus, when paramoecia are kept in a small aquarium 

 under what seems to be appropriate conditions multipli- 

 cation by fission proceeds for a certain time, after which 

 the organisms appear to languish, cease to multiply, 

 become inactive, and tend toward extinction. Indeed, 

 not long after the appearance of these symptoms, the 

 organisms do die and disappear. 



But Maupas observed that if at this critical period 

 the contents of two such aquaria are poured together, 

 a phenomenon known as conjugation quickly takes place. 

 Two organisms, presumably one from each stock become 



