86 On the Natural History of the 



Medusse in one family. He points out the little importance 

 to be attached (except for generic and specific distinctions), to 

 the number of tentacles, and the position of the ovaries in 

 these Medusae. The grand characters of the group or family 

 are as follows: — Consisting of a gelatinous disk with the 

 margin re-entering so as to form a cavity beneath ; a central 

 digestive cavity, from which tubes carrying chyme and form- 

 ing a chymiferous system, radiate towards the margin and 

 connect with or pass into a circular tube situated near the 

 margin ; tentacles and eye specks along this margin ; 

 mouth central, but varying in size and form ; reproductive 

 organs following the chymiferous system ; a nervous ring 

 adjoining the submarginal chymiferous tube ; generation 

 alternate, one form Polypoid, and the other Medusoid. 



Among the species described, we select for particular 

 notice the Hippocrene super ciliaris, the observations on which 

 embrace the principal points determined by the author. 

 This beautiful Medusae is a globular bell- shape animal with 

 four bunches of tentacles on the lower margin. In the inner 

 cavity of the bell, at centre, there is a dark four-sided mass, 

 containing the mouth and the digestive cavity, about as 

 broad as long. In some species, as the genus Sarsia, the 

 mass is elongated into a moveable proboscis, in others it is 

 scarcely projecting. From its angles, in the Hippocrene, 

 proceed internally four tubes, which carry from the digestive 

 cavity the chyme or fluids after digestion, diluted with more 

 or less of the external waters : these tubes pass to the 

 border and here connect with a circular tube which follows 

 the margin around, and in which the chyme continues its 

 course. This, as Professor Agassiz explains with many de- 

 tails, is the circulating and digestive system combined, of 

 this and other species of the family. The tubes may be 

 closed at their connection with the stomach, " shewing that 

 the food is not admitted before it has undergone a certain 

 degree of elaboration ; but no sooner has it been reduced to 

 the requisite degree of fluidity, in which the particles of the 

 nourishing materials appear like little globules, than they 

 open, the nutritive fluid passes into the radiating tubes, cir- 

 culates regularly through these tubes along the inner walls 



