224 BIOLOGY OF THE PROTOZOA 



morphosing parent cell receive a full set of new motile organs com- 

 mensurate with the size of the young organisms. The phenomenon 

 is very striking in forms with giant cirri such as the jumping types 

 of ^\\\Aot\d?e—Diophrys or Uronychia. In the latter genus the 

 great posterior cirri are the most conspicuous organs of the cell 

 (F'ig. 107). The buds which are to grow and replace them are appar- 

 ent before there is other external evidence of the approaching 

 division and even before the nucleus has concentrated into its divi- 

 sion form. At the same time similar buds appear in the division 

 zone, that which is destined to form the giant hooked cirrus appears 

 first and is alwa\'s larger than the others which appear one after the 

 other according to ultimate size. Owing to their minute size it 

 has not been determined whether or not the individual cilium is 

 withdrawn in like manner and replaced by new ones. In some, at 

 least, according to the observation of MacDougall on Chilodon 

 uncinatus (1925) such substitution does take place and it is quite 

 probable that it is universal. The interesting experiments of 

 Dembowska (1925) show that removal of a single cirrus of Stylo- 

 nychia mytilvs causes regeneration of the entire motile apparatus, 

 but no such result follows extirpation of any body region that is 

 free from cirri or cilia. 



The phenomenon is obviously analogous to the absorption and 

 renewal of flagella in the flagellates. Whether or not there is a 

 similar division of the basal bodies of the cilia has not been fully 

 established. 



Other evidence of protoplasmic reorganization at division is 

 furnished by the history of some of the functional metaplastids of 

 the cell. Trichocysts are apparently handed down without change 

 (Fig. 21, p. 53), but there is good evidence that the more compli- 

 cated aggregates of trichites are absorbed and replaced by new ones. 

 This is the case for example in the Chlamydodontidse, where the 

 complex oral baskets are replaced by new ones at each division 

 Enriques, Nagler, MacDougall, et a/., (Fig. 106). 



From this brief survey it is quite evident that far-reaching changes 

 of the protoplasmic organization take place at periods of division. 

 Both nuclei and cytoplasm are necessary but the micronucleus 

 apparently may be lost without destroying the power of the cell to 

 (li\i(le. Emicronucleate races of ciliates, arising possibly through 

 defecti\'e reorganization and division after conjugation (see Moore, 

 1924), have been maintained in culture for many generations by 

 division, although they are ultimately lost (see Chapter X). On 

 the other hand, the power to regenerate is connected in some manner 

 with the micronucleus. Thus young cells of Vronychia tram-fuga, 

 when transected with a scalpel, will regenerate only that fragment 

 which contains the micronucleus (Calkins, 1911, Fig. 108; Young, 

 1923). In old cells, however, both fragments regenerate regardless 



