REPRODUCTION 223 



h. Evidence of Cytoplasmic Reorganization.— Not only is there 

 evidence of chano;e in the cytoplasmic make-up at division through 

 the distribution and absorption of nuclear material as in Vroleptus 

 mohilis, but the entire cytoplasm shows other e\'idence at this 

 period. In all ciliates there is a more or less clear 1\' marked antero- 

 posterior differentiation, the anterior part usually bearins; the mouth 

 and the more or less specialized motile organs for the capture of food 

 or the directing of food currents, while the posterior part is usually 

 much less specialized. Should such a specialized ciliate be cut 

 through the center as Balbiani (1888) did for the first time, the two 

 fragments would be different. The anterior fragment of a Siylo- 

 nychia or Uronychia, for example, would retain the highly differen- 

 tiated parts about the mouth while the posterior part would be 

 relatively undifferentiated. The finer organization or genotype, 

 however, is represented by all of the protoplasm of the cell, and 

 that organization has the ability under proper stimulation, of form- 

 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. 108). 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. 209). 



The processes through which the ciliate cell passes during division 

 indicate that the organism is restored to a generalized condition 

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

 tome the entire array of complex cortical organs is withdrawn and a 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 hjT^otrichous ciliates, has been observed in many forms and is 

 probably characteristic of the entire group. It is most clearly 

 established in the Hypotrichida where 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 

 continues and at the same time minute buds of protoplasm appear 

 at the bases of these disappearing membranelles. These buds grow 

 pari passu with the dwindling motile organs until finally the latter 

 are entirely absorbed and the buds have developed into functional 

 membranelles. In the same way each cirrus is replaced by a new 

 growing bud quite regardless of the position in anterior or posterior 

 half. Undulating membranes are similarly withdrawn and replaced 

 bv new ones so that the \'oung cells formed hv division of the meta- 



