248 C. M. CHILD. 



tissue will be found extending across parts of the opening. 

 While growth undoubtedly begins on all parts of the cut surface, 

 this membrane becomes distinct earlier at those regions where 

 the cut edges are most closely approximated. Frequently when a 

 piece is opened in the manner described the membrane will be 

 found extending across regions corresponding to certain of the 

 wrinkles about the opening but not yet covering the central area. 



This method of formation of the thin membrane closing the 

 end is well shown in a piece cut from a specimen of C. incni- 

 branaccus. In this species the body-wall is so thick and stiff 

 and the diameter of the body so great that in short pieces the 

 infolding of the ends is often not sufficient to close the opening. 

 In Fig. 6 a piece of this kind is shown. The new tissue first 

 became evident along the fold a, and a day or two later a thin 

 membrane was spread across this fold (Fig. 7, a. The new tis- 

 sue is stippled). A little later still the fold at b (Fig. 7) also 

 showed a thin membrane (Fig. 8), which, however, was after- 

 ward ruptured by contractions of the piece due to the stimulation 

 incidental to examination. In Fig. 8 it is seen that the new 

 tissue is gradually spreading over the opening from a. In Fig. 

 9 the opening is nearly closed. Several days later closure was 

 complete. The changes in form of the piece as shown in the 

 figures were the result of stimulation caused by the manipulation 

 necessary for examination and drawing. In C. soliianns if the 

 pieces are allowed to remain undisturbed at ordinary summer 

 temperature the openings at the ends are usually completely 

 closed by the thin membrane on the third day after operation. 

 In the piece from C. membranaceus above described closure was 

 complete after twenty-seven days. In general this species re- 

 generates much more slowly than C. so/it arias, but here the 

 closure was exceptionally slow. 



The membrane is easily ruptured by the contractions of the 

 piece when strongly stimulated and great care is always necessary 

 in the examination of such pieces to prevent rupture. In conse- 

 quence of contraction the different parts of the margin change 

 their relative positions or the mass of the mesenteries and fila- 

 ments exerts pressure from within, thus readily causing rupture. 



There is little difference as regards time of closure between the 



