784 MORPHOGENESIS 



almost immediately, whereas large-scale operations involving some of 

 the kinetic organelles are apt to incite breakdown changes that lead to 

 the resorption of the entire ciliary apparatus (Fig. 180). Extreme cases 

 were reported by Dembowska {Stylonychia, 1925; Uronychia and Sty- 

 lonychia, 1926) and Taylor [JJronychia, 1928) in which the removal 

 of a single cirrus or even severe injury to its basal plate is sufficient to set 

 in motion the entire regenerative functions. External portions of the 

 giant cirri on JJronychia may be excised with none of these consequences 

 (Taylor). 



For those hypotrichs studied by Dembowska (1926) and M. E. Rey- 

 nolds (1932), the duration of the regenerative process is independent 

 of the degree of injury, requiring from three to five hours for complete 

 restitution in all cases. The time interval between cutting and the initia- 

 tion of reorganization varies for different genera. Generally, the greater 

 the injury, the shorter the interval. 



Tittler's (1938) experiments on Uroleptus mobilis were designed to 

 test whether or not ciliates injured or mutilated by high-tension currents 

 undergo reorganization and regeneration comparable to that which fol- 

 lows other types of mutilation. The induction current caused most of 

 the organisms to migrate toward the cathode of the break shocks. Ap- 

 proximately 75 percent of the exposed organisms were vacuolated or 

 deformed at the posterior end, i.e., the extremity nearest the anode. One- 

 minute exposures sufficed to produce many fragments with posterior de- 

 ficiencies and a few with anterior injuries. Regeneration, accompanied by 

 a complete de- and redifferentiation of cortical organelles and macro- 

 nuclear reorganization, was the rule. Most of the reconstituted individuals 

 were ready to divide within thirty-four hours after treatment. The de- 

 stroyed micronuclei were replaced from those remaining. Nuclear clefts 

 appeared in the intact macronuclei; the latter fused into a single mass 

 before constricting into the eight parts which characterize the normal 

 individual. 



5. THE SIZE FACTOR 



Surprisingly large portions of the cytoplasm may be removed from 

 most Protozoa without permanently impairing the vital processes; under 

 favorable growth conditions, complete regeneration occurs within a rela- 

 tively short time. Moreover, the regenerative capacity can be tested fur- 

 ther by repeated excisions, so that the reparative processes are made to 



