1 6 Invertebrate Zoology. 



Can you trace an opening leading from the mouth into 

 a central cavity? There are radiating chymiferons tubes 

 leading from the base of the cavity of the manubrium to the 

 periphery of the disc, where they open into the very delicate, 

 circular, circumferential canal} Is the arrangement of the 

 chymiferous tubes and the marginal tentacles correlative? 



The Sexual Reproductive Organs lie one on each radiating 

 chymiferous tube, and appear, when viewed from below, as 

 wart-like projections. Their contents, as eggs or spermatozoa, 

 are dehisced into the sea-water. 



The Nervous System and Sensory Organs. A circu- 

 lar nervous tract consisting of a plexus of nerve cells extends 

 entirely around the margin of the umbrella. Fibrillae extend 

 from the edge of this "ring" to muscle fibres and to certain 

 marginal sense-organs. The latter may be tactile, " audi- 

 tory " or visual. The tentacles are the principal tactile 

 organs. The so-called " auditory vesicles ' are probably 

 organs of equilibration, and medusae being thus provided are 

 called vesiculate, while those having pigmented visual spots 

 are called ocellate. The visual spots are more frequently 

 found at the bases of the perradial tentacles. 



Make drawings that will show the important points in the 

 anatomy of the Hydromedusa. 



1 The chymiferous tubes are more frequently four in number and 

 determine four radii {perradii) of the umbrella. In certain Campanu- 

 larians, however, there are eight or more of these radiating tubes. 





