48 



HANDBOOK OF INVERTEBRATE ZOOLOGY. 



manubrium the ectoderm cells are again 



/. On the 

 thickened, and have a few scattered nematocysts. 



Fig. 25. 



Fig. 25. — Diagram to show the ari-angement 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 chymiferous tube on the right side, 

 and through the space between the tubes on the left. 



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

 umbrella. /. Manubrium. g. Oral tentacles. /*. Radial tentacle. 

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

 productive organ, rn. 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 endodemi (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. 



J 



