AURELIA 57 



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 

 Hydromedusa. 



7. At the marginal extremity of each perradial 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, clublike struc- 

 ture containing a prolongation of the radial canal. At its 

 outer extremity are calcareous concretions or lithites, and a 

 pigment spot or ocellus. Each tentaculocyst is covered abor- 

 ally by a hoodlike projection, and on the sides by marginal 

 lappets. 



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

 taculocyst. These have been assigned olfactory functions, and 

 are called the olfactory pits. Evidence of function is lacking. 



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 planulae. Most of the eggs are set free in the water, 

 where they develop. 



The planula after swimming for some time attaches by 

 one end, acquires a coelenteron, mouth, and tentacles. Longi- 

 tudinal ridges called taeniolae or taenioles are formed in the 

 coelenteron, septal funnels are formed between the tentacles 

 and mouth, and from the septal funnels ectoderm cells are 

 budded off that form the four longitudinal septal muscles. 

 This larva is called a scyphistoma. 



