General Morphology of the Protozoa 49 



posedly concerned mainly with reproduction and sexual phenomena and 

 therefore is primarily of genetic interest. The occurrence of apparently 

 amicronucleate strains in several species — Oxytricha hymenostoma (41), 

 Oxytricha fallax, Urostyla grandis (234), and Tillifia magna (4), among 

 others — suggests that the micronucleus is not actually essential to giowth 

 and fission. Observations on the regeneration of fragments (2) indicate 

 that the macronucleus is essential for complete regeneration of ciliates. 

 The importance of the micronucleus apparently varies with the species. 

 Some species fail to grow, or even to regenerate, without a micronucleus, 

 while macronucleate fragments containing no micronuclei have given rise 

 to amicronucleate races in other species — Stentor coeruleiis (201) and 

 Oxytricha fallax (9), for example. 



Dispersed nuclei 



So-called dispersed nuclei have been described in certain Protozoa, 

 although the older accounts have not been confirmed in more recent 

 investigations and such interpretations were undoubtedly based upon in- 

 adequate cytological techniques. However, the ciliate Dileptiis has been 

 cited for many years as an example in which chromatin granules, scat- 

 tered through the endoplasm, are the substitute for a nucleus. The con- 

 dition in Dileptus gigas has been analyzed by Visscher (216). During post- 

 conjugant reorganization the synkaryon divides into two nuclei, one of 

 which produces 32-64 micronuclei, and the other a comparable number 

 of macronuclei. The latter eventually divide further into the many scat- 

 tered inacronuclear derivatives characteristic of the normal ciliate. The 

 nuclear apparatus of Dileptus anser (81) may include as many as 200 small 

 macronuclei measuring 2-3[x and containing fine Feulgen-positive gran- 

 viles. A few of the macronuclei can usually be found in division at almost 

 any time, but they all seem to divide almost simultaneously just before 

 binary fission. 



LITERATURE CITED 



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