﻿OF THE ACALEPH/E OF NORTH AMERICA. 317 



of the chymiferous cavity is identical with the position of a similar peduncle observed 

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

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

 Medusae, 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 ambulacra] tubes of Beroe and the vertical chymiferous tubes of the naked- 

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

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

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

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

 which they are carried out in their 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 Diseophorae. 



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

 the Discoid Medusae. 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 

 Ophiura. They are essentially the same. Above the black eye-speck in the 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 

 the 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 



