OF THE ACALEPHiE OF NORTH AMERICA. 317 



of the cliymiferous cavity is identical with the position of a similar iieduncle observed 

 most easily in young Sarsiae soon after their separation from their Corynoid stem. The 

 circumstance, that at this extremity the cliymiferous cavity has two openings in Beroid 

 Medustc, does not institute between them and the common Discoid type a greater differ- 

 ence than exists between the star-fishes with a central anus and those which are deprived 

 of this aperture, and cannot on that account be considered as establishing a radical dif- 

 ference between the structure and arrangement of the main systems of the body in the 

 two families. On the contrary, the circumstance, that here eight tubes, probably in 

 connection with the central cavity, diverge towards the periphery, to extend vertically 

 along its walls, and gradually to enlarge along the sides, establishes a close resemblance 

 between the ambulacral tubes of Beroe and tiie vertical cliymiferous tubes of the naked- 

 eyed Discophora;. Again, the circumstance of their uniting to form a circular tube 

 around the periphery may be compared to the circumstance of the ambulacral tubes meet- 

 ing in tiie peripheric horizontal tubes arising from the main central cliymiferous cavity. 

 There are differences in the number of parts, and slight differences in the manner in 

 whirli they are carried out in tiieir adaptation ; but, on the whole, the relations between 

 the mouth and digestive cavity proper, the central embryonic tubercle, and the chymif- 

 erous tubes, are essentially the same in the Beroid Medusae and the Discophorie. 



There are some further complications in the Beroid, which are not yet carried out in 

 the Discoid Medusa. We shall see that Bolina in this respect is even still more -com- 

 plicated than Pleurobrachia. But this no more changes the fundamental relations, than 

 the complicated ramifications of Astrophyton change the relations of that genus to 

 Ophiiira. They are essentially the same. Above the black, eye-speck in tiie natural 

 position of Pleurobrachia, or below it in those Beroid Medusae in which the anal ex- 

 tremity of the animal is turned upwards, as in Bolina, there is a tubercle or gan- 

 glion-like mass of larger size than the black speck itself, consisting of heterogeneous 

 elements, which seems to be encircled by a tube some way or other connected with 

 the eight narrow converging ambulacral tubes, on the anterior and posterior side of which 

 are seen four smaller tubercles or swellings, between which arise two threads rapidly 

 diverging forward and backward, and extending into the circumscribed area. I can 

 offer only suggestions respecting these parts, and must leave it for future investiga- 

 tions to decide what they are in reality. I am, however, inclined to suppose that 

 tlie circle at the base of the ganglion is a vascular or chymiferous ring, answering 

 to the ring observed above the proboscis in Sarsia, and I expect it will be proved 

 that the eight narrow tubes connected with the ambulacral tubes arise from this 

 circle, or empty into it. The four swellings in advance of and behind the tubercle 



