344 Vniversitij of California Publications in Zoology [Vol.20 



The neuromotor system of Paramaecium, therefore, as has been 

 demonstrated by the foregoing description of the neuromotor center 

 and the peripheral and cytopharyngeal fiber systems, is, from a 

 morphological point of view, a structurally adapted, coordinating 

 mechanism. It is easily compared with a metazoan nervous system, 

 being composed of fibers that connect the organelles of locomotion, 

 nutrition, and defense with a definite center. 



The Neuromotor System during Division 



One is surprised in reading the literature of Paramaecium to find 

 only two accounts of the fate of the old cytostome and cytopharynx 

 in dividing animals and of the origin of new ones. One of these is 

 quoted by Doflein (1916) from R. Hertwig (1890). The old cytostome 

 is represented as budding off a new one which becomes the cytostome 

 of the posterior daughter. 



The second account is by Child (1916) who finds that the old 

 cytostome and cytopharynx are dedifferentiated and disappear. Jen- 

 nings (1908) had previously observed the same process, also the 

 occurrence of a slight shortening of the body in animals about to 

 divide. The new cytostome and cytopharynx of the posterior daughter 

 are redifferentiated in the position occupied by the old cytostome. 

 The cytostome and cytopharynx of the anterior daughter are entirely 

 new structures (figs. C, D, E). 



The accuracy of this account I verified with only a 16-millimeter 

 objective and 2Qx oculars when animals from a rapidly dividing 

 culture were transferred to a Syracuse watch glass. Dividing 

 animals usually remain attached to some debris in the bottom of the 

 dish during the entire process. In one case observed, the entire 

 process from the time division became manifest to the separation of 

 the two daughter animals required forty-five minutes. 



A complete account of the changes in the neuromotor apparatus 

 during the division process cannot as yet be given. It is certain that 

 the cytostomal and cytopharyngeal fibers of the anterior daughter 

 are new structures, as they appear very soon after the constriction 

 (pi. 34, fig. 20). Since the origin of a new cytostome gives rise to a 

 new center, it is likewise certain that the peripheral fibers of the 

 anterior daughter are to a very large extent newly formed. But since 

 the fibers, other than those of the cytopharynx, were not seen in the 

 stained animals in division, the extent to which dedifferentiation 

 and redifferentiation occurred in the peripheral fibers of the posterior 

 daughter has not been ascertained. 



