NOTES ON REGULATION IN STYLARIA LACUSTRIS. l8l 



DESCRIPTION OF FIGURES. 



FIG. I. (a, b, c.) Redifferentiation of a zone of fission. In (a], a zone is 

 formed and there is a constriction in the body-wall. The intestine in this region is 

 transparent, devoid of pigment. In (b) and (<:) the zone and constriction have 

 disappeared and the intestine becomes pigmented. The accumulation of transparent 

 embryonic tissue before and behind the septum in (), mentioned in the text, is not 

 indicated in the figure. The ectodermal thickening is indicated at the constriction. 

 In this and all the figures the dorsal capilliform setae are not represented full length. 



FIG. 2. Fragmentation of the eyes after mutilation. The prostomium was sev- 

 ered and a short longitudinal cut made in the first segment. The direction of the 

 cut indicated by line. The condition in (/;) was observed three days after the muti- 

 lation. The slightly curved outgrowth of the bud of the prostomium is an unusual 

 occurrence. 



FIG. 3. Regeneration from first segment, resembling a repetition of the head seg- 

 ment, of less diameter. The line indicates direction of the cut. The eye is regen- 

 erated. The condition here represented was fifteen days after the operation. 



FIG. 4. Failure of regeneration after an oblique cut through first segment. In () 

 the condition twenty-three days after the operation is shown. The eye is not regen- 

 erated and there is no trace of a prostomium. 



FIG. 5. Failure of regeneration in first segment. The eye in (b) is fragmented 

 into two portions. Later it became normal. 



7. Absence of regeneration in short posterior pieces. 



With the purpose of finding whether heteromorphosis would 

 take place, as in the earthworm, in the case of very short pos- 

 terior pieces a number of experiments were tried with as short 

 posterior pieces as would survive the operation. No tails appeared 

 on the anterior ends. A number of pieces which survived the 

 operation for as long a time as three weeks, did not regenerate 

 the anterior ends. During the first week these pieces elongated 

 within the budding region in front of the anal segment. The 

 immature segments became further differentiated, their setae in- 

 creasing in size, but no new segments appeared. The pieces then 

 appeared to be composed of segments nearly equal in size, and 

 there was no zone of embryonic undifferentiated tissue remaining. 

 One such piece was obtained by a cut one segment behind the 

 pharynx of a posterior zooid. It contained at first a region com- 

 posed chiefly of indistinct segments. At the end of a week these 

 segments had increased in length and their setae had grown until 

 twenty segments could be easily counted. Its size was greater 

 than that of a minimal piece capable of regeneration taken from 

 the middle of the body. It showed no trace of anterior regen- 

 eration for three weeks, but was still active in its movements. Un- 



