NOTES ON REGULATION IN STYLAR1A LACUSTRIS. 1/5 



regeneration of the pharyngeal region of five segments from an 

 anterior cut surface. Similarly, the anal segment is regenerated 

 from a posterior cut surface, but within a shorter time. In re- 

 generation a bud or knob of transparent embryonic tissue is first 

 proliferated, which increases in length, develops a prostomium, 

 and becomes segmented within a few days. Section within the 

 anterior specialized region is followed by the restoration of the 

 number of segments which were removed, from one to five. 



Thus it is seen that the pharyngeal region of five segments is 

 the unit of regeneration after section within the trunk region, 

 and the process is identical with the normal or physiological 

 regeneration that occurs in self-division. On the other hand, the 

 segments are the units of regeneration when the mutilation is 

 within the pharyngeal region. 



There is a close analogy between these results and the obser- 

 vations made upon the earthworm, in which four or five seg- 

 ments are regenerated after more than five are cut off. 



The prostomium has great power of regeneration. Frequent 

 cases are met with of forms with regenerating prostomium. Child 

 ('oo) figured a specimen found in nature with a forked prosto- 

 mium which was doubtless a product of regeneration. In Fig. 9 

 is shown a somewhat similar case of regeneration of the pro- 

 stomium following the severing of the organ at the base ; in this 

 case the organ is doubled. In later stages the lateral bud was 



O ~J 



absorbed. 



2. Regulation of the intestine behind a cut surface to form the 



o 



oesophagus and crop. 



It was stated at the outset that this paper deals chiefly with 

 certain processes of regulation accompanying regeneration proper. 

 As an excellent example of the general regulative changes ac- 

 companying regeneration in this worm a case of regulation may 

 be mentioned which occurs normally in the process of self-division 

 or physiological regeneration as well as in cases of regeneration 

 after injury. The oesophagus and crop occur in the sixth to 

 eighth segments, i. c., not in the region which is formed from 

 new tissue by proliferation. Hence the oesophagus and crop 

 must be formed by a process of regulative transformation of the 

 intestine behind the new proliferating tissue. This involves a 



