MORPHOGENESIS 789 



Garnjobst (1937) found evidence of secretory activity on the part of 

 enucleate fragments of Stylonethes. Cyst formation after injury is the rule 

 in this species. In one case a cyst wall was produced by a fragment which 

 contained no nuclei. 



The possibility of regeneration in Infusoria is not precluded by the 

 absence of either micronucleus or macronucleus. It is difficult, however, 

 to formulate any satisfactory conclusion at this time, inasmuch as ob- 

 servations on different species often present contrasting results. In spite 

 of the accumulated literature, the respective roles of each of the di- 

 morphic nuclei remain uncertain. 



Gruber (1886) regarded the micronuclei in Stentor as of secondary 

 importance, since no regeneration occurred until a macronucleus dif- 

 ferentiated from one of the amphinuclear products. Lewin (1910) 

 agreed with Gruber and did not believe the micronucleus necessary for 

 growth or regeneration in Paramecium caudatiwi. On the contrary. Cal- 

 kins (1911b), Peebles (1912), and Schwartz (1934) obtained re- 

 generates in this species only when both types of nuclei were present. 



In Stevens's (1903) experiments on Lichnophora auerbachii, a species 

 with a beaded macronucleus and one micronucleus, regeneration was 

 limited to the production of a few oral cilia [in situ), new peristomes, 

 and relatively small segments of the attachment disc. She showed that 

 only pieces including the attachment disc, the neck, a quarter section of 

 the oral disc, and representatives of both nuclei were capable of re- 

 generating "fairly normal" individuals. Isolated oral discs (amicro- 

 nucleate) and basal discs (with micronuclei) never regenerated, al- 

 though they survived for several days. More recently, Balamuth (MSS, 

 1939) studied regeneration in L. macjarlandi and found its regenerative 

 capacity to be greater than Stevens showed, since isolated amicronucle- 

 ate oral discs definitely replaced injured adoral zones. Missing basal 

 discs were not regenerated in L. macjarlandi, but it was pointed out that 

 the two daughter basal discs form in this genus only by division of the 

 corresponding parent structure. 



Calkins (1911a) and D. B. Young (1922) described regeneration 

 in amicronucleate fragments of Uronychia when the operations were 

 made very late in the interdivisional period. The regenerates usually be- 

 came abnormal after three to four days; they apparently starved to death 

 for, according to Young, no food was ingested or assimilated. The frag- 



