



CAMPANULARIAN HYDROID. 



to trace in a young specimen, but more distinct in old 

 ones. The circular chymiferous tube is so small that it 

 can only be seen at all under the most favorable circum- 

 stances. 



4. The reproductive organs (Fig. 27, d) on the lines of 

 the radiating tubes, about half-way between the centre and 

 edge of the umbrella. 



5. The small epithelial cells which cover the surface of 

 the sub-umbrella. 



6. The velum (Fig. 27, </) is very narrow, and is usu- 

 ally stretched over the bases of the marginal tentacles. 



1. Notice the small, flat, epithelial cells which cover it, 

 and pass, by a gradual transition, into the rounded ' ecto- 

 derm cells which cover the bases of 

 the tentacles. 



7. The auditory organs (Fig. 

 27, /) consist of a nearly spherical 

 capsule, attached to the outer sur- 

 face of the velum close to the base 

 of a tentacle, and containing a cen- 

 tral highly refractive, spherical oto- 

 lith. 



IV. Examine one of the auditory 

 organs with a high power five or 

 six hundred diameters and no- 

 tice : 



FIG. 28. Otocysts of Euchilota ventricu- 

 laris, magnified four hundred diameters; from 

 an osmic acid specimen. (Drawn from nature 

 by W. K. Brooks. ) 



a. Supporting layer, b. Outer layer of 

 epithelium, c. Inner layer of epithelium. 

 d. Otolith. e. Velum. /. Cavity of Otocyst. FIG. 28. 



a. The capsule (Fig. 28). This consists of 

 layers. 



