AURELIA. 37 



branch on either side. One portion of the per-radial canal con- 

 tinues straight to the margin and joins the circular canal, without 

 further subdivision, but the two side branches in turn subdivide 

 several times. 



(b) From the peripheral wall of each gastric pouch three 

 canals pass toward the margin; the middle one (inter-radial 

 canal) branches somewhat after the manner of the per-radial 

 canals, but the other two (ad-radial canals) continue to the cir- 

 cular canal without further branching. 1 



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 

 development may frequently be found adhering to the oral 

 aims. 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. 



1 In most cases the foregoing canals are very evident, but if they are 

 not, they may be injected with water in which powdered carmine is mixed, 

 by inserting a large-mouthed pipet into the stomach. 



