90 LEWIS R. GARY. 



mesenteries are present while a member of the third pair has made 

 its appearance on one side of the longitudinal axis of the sto- 

 modeum. 



In Fig. n, a section taken through the embryo near the base 

 of the stomodeum, seven mesenteries are present. The same 

 four as noted in the previous section are complete while both 

 those of the third pair are present and one of the fourth pair is 

 seen as a slight prominence of the endoderm containing a very 

 thin mesogleal fold. In Fig. 12 only six mesenteries are present, 

 but it seems that one of the third pair is lacking instead of the 

 single one of the fourth pair which was seen in the previous section. 



The first pair have already acquired their mesenteric filaments, 

 which at this stage extend only a short distance below the 

 stomodeum. 



Farther down, at the level of the section shown in Fig. 13, 

 only four new mesenteries are present, while seven of those which 

 came over in the laceration piece from the parent are seen. 

 This last-mentioned section was taken about one third of the 

 distance from the oral disc to the base of the embryo, and in this 

 series the newly formed mesenteries are found in only four of 

 the following sections. 



In the sections shown in Fig. 14, all of the mesenteries present 

 are those which were in the laceration piece at the time when it 

 was separated from the parent. Fig. 14, although taken at 

 some distance from the base shows, in comparison with the pre- 

 vious sections, that the basal portion of the embryo is of con- 

 siderably greater diameter than the more distal portions. 



A comparison of the three last-mentioned figures illustrates 

 one phase of the redistribution of materials in the growth of a 

 laceration embryo. In Fig. 13, that side where the new mesen- 

 teries are being formed is very thin-walled, the mesoglea having 

 become reduced to a thin sheet throughout that half of the body. 

 In the remaining half, on the other hand, the tissue relations of an 

 adult Aiptasia are still maintained. In the sections through the 

 more proximal part of the body the adult tissue relations are 

 apparently undisturbed, at least morphologically. It will be 

 seen, however, that in this region there has been coincident with 

 the elevation of the oral end of the embryo a drawing together of 



