REPRODUCTION 



221 



ing all of the differentiated parts of the entire adult organism. By 

 regeneration, therefore, such a cut individual replaces the charac- 

 teristic structures of the posterior end by the anterior fragment and 

 the characteristic structures of the anterior end by the posterior 

 fragment (Fig. 113). By their usual method of transverse division 

 the ciliates have quite a different inheritance than do flagellates 

 which divide longitudinally. In the latter the highly differen- 

 tiated anterior ends and the less differentiated posterior ends are 

 equally divided so that the daughter cells have a like inheritance 

 (p. 95). 



Fig. 



111. — Uronychia Iransfuga with giant cirri, membranelles used in swimming, 

 ten macronuelear segments, and single micronucleus. (After Calkins.) 



The processes through which the filiate cell passes during division 

 indicate that the organism is restored to a generalized condition 

 practically equivalent to an encysted cell. Except for the cyto- 

 stome the entire array of complex cortical organs is withdrawn and 

 a new set is formed from the cortical protoplasm. This significant 

 process first described by Wallengren (1900), later by Griffin (1910) 

 in hypotrichous ciliates, has been observed in many forms and is 

 probably characteristic of the entire group. It is most clearly 

 established in the Hypotrichida w T here the highly specialized and 

 conspicuous motile organs furnish suitable material for study. 

 According to Wallengren's description the membranelles of the 

 adoral zone slowly decrease in length as the process of absorption 



