PEDAL LACERATION IN ACTINIANS. 9! 



the basal portion so that it is now nearly circular in outline. 

 In Fig. 15 it may be seen that the old mesenteries which formerly 

 occupied only one side of the fragment at the time of its sepa- 

 ration from the parent have now come to be distributed so 

 that they now arise from about four fifths of the c'rcumference. 



In sections through an older specimen, as shown in the series 

 of figures from Fig. 15 to Fig. 18, the second set of mesenteries 

 has made its appearance about the inner surface of the oral disc, 

 and eighteen of them have reached the stomodeum. Farther 

 down along the stomodeum (Fig. 17), the twelve primary mesen- 

 teries are complete while only one other pair has made sufficient 

 downward growth to appear in such a section. 



In Fig. 18, where eleven of the twelve primary mesenteries are 

 present, none of those which came over in the laceration piece 

 from the parent animal are in evidence. Eight of the new mesen- 

 teries have acquired their filaments, but only those on the first 

 pair of mesenteries are trilobed. 



As a basis for the comparison of this series with the previous 

 one attention may be called to the appearance of the mesoglea 

 in Fig. 18. At a corresponding height on the column of the 

 individual shown in the former series (Fig. 14), none of the newly 

 formed mesenteries were present, while in Fig. 13, where only 

 four of them had appeared, that side of the column on which they 

 were situated showed all of the characteristics of newly formed 

 tissue. 



This shows beyond question that in the older specimen the 

 new mesenteries have extended down to a part of the body where 

 there were formerly some of the older mesenteries which by this 

 time have been entirely resorbed. It will be noticed that in this 

 part of the body the tissue readjustment has proceeded until 

 the relation between the layers characteristic for the adult has 

 been reached. 



Carlgren, 1904, in discussing a series of sections through an 

 embryo in which eight of the new mesenteries had reached the 

 stomodeum figures two sections and makes statements from which 

 I can infer only that he understands, either that some of the 

 old mesenteries are brought into the permanent systen of mesen- 

 teries of the laceration embryo, or that some of the new mesen- 



