AURELIA. 39 



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

 Uke 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 

 development 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 

 nematocysts, and they may aid in killing live food taken into 

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

 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 radial canal. At its 

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

 ment-spot or ocellus. Each tentaculocyst is covered aborally 

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



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

 tentaculocyst. These have been assigned olfactory functions, 

 and are called the olfactory pits. Evidence of function is lack- 

 ing. 



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. 



8. If time permits, study developmental stages. 



The eggs are shed through the mouth and frequently be- 

 come entangled in the oral arms, where they may develop into 

 planulse. Most of the eggs are set free in the water, where they 

 develop. 



The planula after swimming some time attaches by one end. 



