48 



HANDBOOK OF INVERTEBRATE ZOOLOGY. 



/. On *the manubrium the ectoderm cells are again 

 thickened, and have a few scattered nematocysts. 



FIG. 25. 



Fio. 25. Diagram to show the arrangement of the layers of the body 

 of a Hydro-Medusa, as seen in a vertical section. The section is repre- 

 sented as passing through a radiating chymiferons tube on the right side, 

 and through the space between the tubes on the left. 



a. Umbrella, c. Velum, d. Aperture of velum. <. Cavity of sub- 

 umbrella. /. Manubrium. y. Oral tentacles. //. liadiul tentacle. 

 i. Radiating chymiferous tube. k. Circular chymiferous tube. I. Re- 

 productive organ, m. Sensory ridge. 



g. The ectoderm of the mouth tentacles is very thin 

 except at their tips, where it forms a knob-shaped battery 

 of nematocysts. 



2. The endoderm (Fig. 25, 2], This layer lines the 

 stomach and chymiferous tubes, and sends solid processes 

 out to the tips of the oral and radial tentacles. 



