172 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. 



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

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

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



Thus, when paramoecia are kept in small aquaria under 

 what seem to be appropriate conditions, multiplication 

 by fission proceeds for a certain time, after which the 

 organisms appear to languish, may cease to multiply, 

 become inactive, and tend to die out. If, however, they 

 are frequently transplanted to fresh sterilized hay-infu- 

 sions, they continue to live and multiply for an almost 

 indefinite period. Thus, Woodruff has been able to keep 

 them alive and in a state of healthy multiplication for 

 2000 generations. Ordinarily, however, when thus kept 

 they die and disappear. 



But Maupas observed that if at the period of decline, 



