GONIONEMUS 65 



(a) Light-perceiving organs. These are large, round, pig- 

 mented bodies at the bases of the tentacles, 



(b) Otocysts, or balancing organs, are small, transparent, 

 ovoid bodies located between the tentacles. In Gonionemus each 

 otocyst consists of a large vesicle surrounding the true sensory 

 organ which is located at the end of a short stalk extending into 

 this vesicle. The rounded structure at the end of the stalk con- 

 tains a cavity, the secondary vesicle, within which a small cal- 

 careous body called the otolith is located. 



8. Make drawings, (a) from the oral surface, 70 mm. 

 (without tentacles), filling in outline one comi)lete tentacle and 

 bases of one-third of remaining tentacles, 



(b) Of an optical vertical section through the radial canals. 



(c) A portion of a tentacle much enlarged, showing sucking 

 disc. 



(d) An otocyst much enlarged. 



9. Make a brief word diagram showing in a circle the life 

 history of a hydrozoan. 



REFERENCES 



Perkins, H. F., 1903. The development of Gonionemus mur- 

 bachii. Proc. Acad. Nat. Sci, Phila. 54 :750-790. 



Thomas, L, J., 1921. Morphology and orientation of the oto- 

 cysts of Gonionemus. Biol. Bull., 40 :287-296. 



