7<3 C. M. CHILD. 



finally complete. In these figures only one end has been shown ; 

 usually, however, closure proceeds from both ends, and the mid- 

 dle portions are the last to become united. 



It is evident that in a spirally or transversely rolled piece this 

 process can never occur, for even if it begins in some fold or local 

 approximation of the cut surfaces it cannot continue, because 

 approximation of the cut surfaces to a degree sufficient to permit 

 their union by new tissue is impossible as long as the piece 

 remains spirally or transversely rolled. 



Description of all possible cases of closure of pieces cannot of 

 course be attempted. Results depend so largely on chance, that 

 every piece affords, it might almost be said, a different solution of 

 the problem. The examination of hundreds of pieces has, how- 

 ever, convinced me that the essential features of the process are 

 those described above. 



The cut surfaces appear to remain capable of giving rise to new 

 tissue for an indefinite period. Often closure of pieces slit open 

 longitudinally is completed only two or three months after sec- 

 tion ; yet during all this time the cut surface retains the power 

 of producing new tissue under proper conditions, though it has 

 no power to produce anything more than the proliferation con- 

 nected with healing, provided it is not in contact with another 

 surface. Union is as complete and perfect, though perhaps not 

 as rapid, when it occurs two months or more after section as 

 when it occurs within a few days. 



When we compare C. solitariits and C. membranaceus we find 

 that in the latter species the thin membranous growth of new tis- 

 sue if once begun between cut edges in contact, may continue 

 until it forms a connecting membrane between widely separated 

 cut surfaces ; in C. solitaries , on the other hand, the membrane 

 is incapable of bridging over spaces so wide ; the new tissue 

 ceases to extend long before a point is reached where the cut 

 surfaces are so widely separated. This difference is so marked 

 that it raises the question as to whether there is a fundamental 

 difference in the conditions and method of growth of new tissue in 

 the two species. Figs. 6-9 of paper I. ('03^) and Fig. 31 of 

 the present paper (an aboral end) illustrate the closure of open- 

 ings in C. membranaceus. In Fig. 31 the new tissue which is 



