NOTES ON REGULATION IN STYLARIA LACUSTRIS. 



I8 5 



10 C. 



10 d. 



DESCRIPTION OF FIGURES. 



FIGS. 6 and 7. Failure of anterior regeneration in case of very short posterior pieces. 

 Fig. 6 represents such a piece twenty-three days after it was severed, Fig. 7 a piece 

 eighteen days after it was severed. It measured 1.25 mm. Further observation 

 was prevented. 



FIG. 8. Regeneration of a double-headed individual. The line in (a) indicates 

 direction of cut. The smaller head was apparently destined to be absorbed at last 

 observation. The specimen was lost before regeneration was complete. Stages (a) 

 and (^) were six and ten days after the cut was made. 



FIG. 9. Regeneration of abnormal prostomium, a doubling of the organ. Later 

 the lateral bud was absorbed. 



FIG. 10. Regeneration occurring in a direction normal to the cut surface. (&) 

 represents the condition three days after the operation, (d] the complete regeneration. 

 In (</) the right dorsal bundle of setae is not restored. In (c) scattered pigment 

 cells resembling the chloragogue cells are present in the new tissue. 



II. REGENERATION OF THE SEXUAL FORMS. 

 The sexual organs of Stylaria come to maturity during the 

 months of October and November. In the height of the sexual 

 stage the animals cease to multiply asexually. In the earlier 

 stages budding animals are frequently seen. In the fully de- 

 veloped sexual animal the formation of new segments in the 

 anal proliferating region also ceases. As a result the animals 

 attain larger size, since the segments in the budding region 

 become fully differentiated. The clitellum is conspicuous, cover- 

 ing the fifth and sixth segments, in which the testes and ovaries 

 lie. This part becomes more opaque and loses its setae. 



