66 



C. M. CHILD. 



needles collapse occurred at once, but was followed by renewed 

 extension in a short time. Pieces with tentacles and disc intact 

 show these changes much better than others, since the phenom- 

 ena of distention and collapse are especially conspicuous in the 

 tentacles. Moreover, in these pieces the presence of the mouth 

 permits much more rapid entrance of water than is possible in 

 pieces with oral end removed, since in these latter there is no 

 apparatus for forcing the water into the enteron. The rapid 

 distention of pieces under the conditions described is made pos- 

 sible only by the ectodermal slime secretion which under normal 

 conditions forms the tube. 



The manipulation incidental to section of the body and the 

 stimulus of the cut itself cause a rapid secretion of this slime 

 during the operation and for some time after. The secretion is 

 tenacious even when first formed and clings closely to the body. 



After inrolling has occurred at a cut surface only ectoderm is 

 visible from without and where different parts of the inrolled 

 margins are in contact the contact is usually in part ectodermal. 

 The slime is secreted over this inrolled portion and forms a 

 tenacious coating which closes all the crevices between the in- 

 rolled portions of the body-wall. Thus, so far as the escape o 

 water in appreciable quantities is concerned, the cut end may be 

 closed within a short time after section, almost as soon, in fact, 

 as the inrolling is completed. 



If the piece is left undisturbed the slime accumulates and the 

 closure becomes more and more complete until finally the thin 

 membrane of new tissue constitutes the definitive closure. If at 

 any time before the definitive closure the slime be carefully 

 removed with needles without causing violent contraction or 

 changes in form of the piece, collapse will occur at once, showing 

 clearly that the slime alone prevented the escape of the water. 



THE GROWTH OF NEW TISSUE FROM THE CUT SURFACE. 



The closure of the ends by new tissue was briefly described in 

 the first paper of the present series, but the conditions which 

 determine it were not discussed. 



As described, the course of the process at both oral and aboral 

 ends in typical regeneration is as follows : First the appearance of 



