MORPHOGENESIS 811 



nerve fiber, a break in the neuromuscular cord does not cause degeneration 

 in either of its separated parts. The motor reactions of the cells joined 

 by the distal segment of the cord are well integrated, but independent 

 of those connected by the proximal portion. The cord alone, rather 

 than the entire stalk structure, appears to be the medium through which 

 regenerative functions are coordinated. Preliminary experiments have 

 shown that a local injury to the protoplasmic portion of the stalk physio- 

 logically divides a colony. The distal part, with its original apical 

 cell, continues to develop as before, whereas one of the cells on the 

 proximal (basal) portion differentiates into an apical cell the activity of 

 which produces another dominant growth axis (Fig. 187). How the 

 single apical cell regulates developmental functions in the distantly 

 separated cells, through the agency of the slender protoplasmic thread, 

 remains as one of the more important problems that invite attention to 

 these colonial Protozoa. 



We are far from having more than an elementary notion of what 

 goes on within differentiating cells, but it is probable that the recent 

 developments in other more specific phases of cell physiology presage 

 a period of keener interest in the age-old problems of growth and form 

 determination. Most of the publications on regeneration now extant 

 are important in substance, but lack the specificity of detail which 

 characterizes the newer contributions on nutrition, respiration, and so 

 forth. They also indicate ( 1 ) the advisability of more carefully planned 

 pre- and post-operative culture techniques, wherein a better evaluation 

 of extrinsic factors is possible; and (2) the value of critical distinction 

 between the failure of cells to survive an experimental procedure and 

 their failure to regenerate. 



Literature Cited 



Alverdes, Friederick von. 1922. Zur Lokalisation des chemischen und therm- 



ischen Sinnes bei Paramecium und Steritor, Zool. Anz., 55: 19-21. 

 Balamuth, W. 1939. Studies on regeneration in Protozoa. I. Cytology and 



regeneration of Lichnophora macjarlandi. Univ. Cal. Library, MS, 1939. 

 Balbiani, E. G. 1888. Recherches experimentales sur la merotomie des In- 



fusoires cilies. Rec. zool. Suisse, 5 : 1-72. 

 1891. Sur la regenerations successives du peristome comme charactere 



d'age chez les Stentors et sur la role du noyau dans ce phenomene. Zool. 



Anz., 14: 312-16. 



