AURELIA. 29 



5. The position of the gastric pouches is made clearly mani- 

 fest by the gonads, which lie on the floor of the pouches, as frill- 

 like structures, horseshoe-shaped, with their open sides toward 

 the mouth. The ova or spermatozoa are shed into the stomach and 

 pass out of the mouth. Embryos in various stages of develop- 

 ment may frequently be found adhering to the oral arms. The 

 sexes are separate. On the sub-umbrellar surface, opposite 

 each gonad, is a little pocket, the sub-genital pit, which opens 

 freely to the outside. Whatever purpose this may serve, it 

 does not function to conduct the genital products to the outside. 



6. Parallel with the inner or concave border of each gonad 

 is a row of delicate gastric filaments. These are supplied with 

 stinging cells, and they may aid in killing live food taken into 

 the stomach. These structures are not present in the Hydro- 

 zoan medusa. 



7. At the marginal extremity of each per-radial and inter- 

 radial canal there is an incision on the edge of the animal, in 

 which there are sensory organs. In each incision find : 



(a) A tentaculocyst in the form of a short, club-like struc- 

 ture containing a prolongation of the circular canal. At its 

 outer extremity are calcareous concretions or lithites, and a pig- 

 ment-spot or ocellus. Each tentaculocyst is protected aborally 

 by a hood-like projection, and on the sides by marginal lappets. 



(b) Two depressions, one above and the other below the 

 tentaculocyst. These have been assigned olfactory functions, 

 and are called the olfactory pits. 



Make a drawing showing the profile of the entire animal, and 

 show the structure of at least one quadrant, as seen from the oral 

 surface. 



If time permits study a developmental stage, ^'ephyra,'' and 

 compare it with the adult. 



By way of comparison, examine demonstrations of Cyanea, 

 Dactylometra, Lucernaria, or other forms belonging to this group. 



