92 EKNEST WARHEN. 



thinner, apparently through some dissolving action of the 

 subjacent ectoderm cells. 



In the next stage the plate of ectoderm has grown out 

 into an ovoid swelling which is covered by a very delicate 

 layer of perisarc continuous with the general perisarc. The 

 endodemn follows the ectoderm, and the portion of endoderm 

 (fig. 2, end.) carrying the ovum (0.) passes into the gonangium, 

 and becomes located on one side of the blastostyle. The 

 diameter of the ovum has increased to 17 lu. 



It may be mentioned here that all the figures in the plate 

 are drawn from sections cut in the plane of flattening of 

 the gonangium, with the exception of the following : figs. 7 

 and 18 represent sections at i-iglit angles to the plane of 

 flattening, and fig. 3 is a transverse section. 



At this time the mesogloea between the ectoderm and the 

 area of endoderm in which the ovum occurs becomes thin and 

 evanescent. The ovum gradually separates from the endo- 

 derm, and the ectoderm above becomes modified, divides into 

 smaller cells and forms a kind of cap over it. This cap and 

 the layer of endoderm (fig. 2, end., and fig. 4, g. e.) immediately 

 below the ovum maybe regarded as representing a rudimentary 

 gonophore. 



The distal portion of the ectoderm of the young gonangium 

 consists of tall columnar cells with short pear-shaped granular 

 cells wedged between. This is the beginning of the covering- 

 plate or " Deckenplatte " (fig. 2, c. p.). The coelenteron {C) 

 expands distally and becomes somewhat T-shaped. 



The ovum now enters the ectoderm (fig. 3, 0.), and the 

 covering cap becomes divisible into an inner columnar layer 

 (fig. 4, i. I.) in immediate contact with the ovum, and an outer 

 layer (o. /.) of fiat cells. The slight crack-like space (fig. 3, 

 c. U.) between the two layers is the equivalent of the umbrella- 

 cavity of a medusa, or more complete gonophore, which arises 

 as a split in a distally placed thickening of ectoderm. The 

 ectoderm at the sides of the gonangium gradually contracts 

 away from the perisarc of the gonotheca (fig. 4, .sp.p s^9.o),and 

 outside the flat ectodermal layer (o. /.) of the gonophore theie 



