No. 3.] MORPHOLOGY OF THE ACTINOZOA. 307 



disintegration of certain of the blastula cells. As will be seen 

 later, this disintegration is a normal occurrence, but the time 

 when it makes its appearance seems to vary in different cases. 



Viewed externally, the larva seems to persist in this condi- 

 tion for some time (Fig. 9), but sections show that very impor- 

 tant changes are going on during this apparent rest. These 

 changes consist of the formation of the endoderm by delamina- 

 tion. I was not able to observe the nuclear phenomena accom- 

 panying this process, but there seems little room for doubt that 

 it really is a delamination. It is multipolar in its distribution, 

 and cuts off the peripheral third from the inner two-thirds of 

 each cell (Fig. 12). The outer cells so formed become some- 

 what spherical, are somewhat granular, and show a distinct 

 nucleus. A peculiar feature which characterizes them, and 

 which seems to be invariably present after delamination is 

 completed, is a clear vacuole, larger than the nucleus, occu- 

 pying the central end of each cell ; somewhat similar vacuoles 

 are figured by E. B. Wilson ('83) in Renilla, but what may be 

 their significance is not apparent. The inner or endoderm cells 

 are much larger than those belonging to the ectoderm, and like 

 these are granular with food-yolk, and here and there show a 

 clear vacuole similar to those of the ectoderm cells, but having 

 no definite position in the cell. One peculiar feature of the 

 endoderm cells is the difficulty which exists in observing their 

 nuclei. In specimens in which the delamination is just begin- 

 ning, only a few cells having separated into the endodermal and 

 ectodermal moities, bodies which stain somewhat more deeply, 

 and are as a rule somewhat larger than the yolk-granules-, can 

 be observed scattered about at different levels in the inner por- 

 tions of the wall of the blastula. Only one of these bodies 

 is to be seen in each cell, there being in addition, of course, 

 the nucleus near the periphery, which will eventually belong to 

 the ectodermal moiety. They do not stain nearly as deeply as the 

 peripheral nuclei, but nevertheless I am inclined to believe them 

 to be the nuclei of the endodermal cells, it being evident from 

 the presence of the large vacuole at the junction of the outer 

 and middle thirds of the cells in which they occur that they are 

 quite ready for division (Fig. 1 1). When the delamination is 

 complete, however, these bodies cannot be satisfactorily made 

 i)ut, and the endoderm cells are apparently without nuclei, 



