24 



distinct at the upper end than below, where it disappears 

 into the loosely constituted cell-mass in the interior. 

 The definite cavity of the coelenteron is sometime later in 

 making its appearance. When finally established it is 

 lined with a thick layer of columnar endodermal epithelium. 

 At its bottom it flares out in following the contour of the 

 body-wall, as it appears in figure 14, which shows a late 

 stage, but the same condition of the coelenteron as exists 

 in the newly transi'ormed larva. The figure also shows a 

 thickened core of endoderm which projects upward into the 

 coelenteron as a gastric peduncle (G.P.). This conical 

 mass of cells develops during the later part of the hydra- 

 stage, 



A. TENTACLES . - 



In the later transformations of the developing Go- 

 nionema no definitely determinate periods separate the 

 times of active change. The development-time is variable, 

 depending upon external conditions of food, temperature, 

 etc. In an average larva, however, the first tentacles 

 make their appearance during the third week after the fer- 

 tilization of the egg, or a week after the commencement of 

 the fixed polyp-stage. Two tentacles appear opposite to 



