﻿OF THE ACALEPH^E OF NORTH AMERICA. 251 



a universal character of this family, to multiply alternately by eggs producing polypi- 

 doms, and by buds arising from these stems to produce free Medusa;. The genus Hippo- 

 crene is easily recognized by its hemispherical form, its four bunches of tentacles, with 

 numerous eye-specks at the meeting of the vertical tubes with the circular marginal one ; 

 and also by its quadrangular, pendulous, central digestive cavity, from the margin of 

 which hang numerous branching fringes. This general appearance of Hippocrene is so 

 peculiar, as at first to suggest the propriety of separating it into a distinct family ; but 

 upon tracing the homologies between all parts through the whole family of naked-eyed 

 Medusae, it cannot escape the attention of the philosophical observer, that all these animals 

 form members of a natural, intimately connected series, and that it would be a gross ex- 

 aggeration of the differences which they exhibit to subdivide them into families. The 

 main features are in all the same. There is a central cavity (Plate I. Fig. 1 -4), here 

 somewhat larger and much shorter than in Sarsia, from which arise four radiating chymif- 

 erous tubes which meet along the lower margin, with a circular tube of the same charac- 

 ter, precisely as in Sarsia. Through this system, the digested food is circulated, and the 

 granules floating in liquid move to and fro from what might be called here also a stomach, 

 through the radiating tubes, into the circular one below, and back. There is nowhere 

 an inlet or outlet to this system, excepting through the mouth, which is surrounded by 

 numerous tentacles, branching repeatedly. These tentacles are only the fringed margin 

 of the mouth itself, and should, therefore, not be considered as something peculiar to 

 Hippocrene ; nor is the mouth in any way peculiar, as it forms here, as in all other 

 naked-eyed Medusae, a circular radiating opening. 



The most striking generic peculiarity of this type is the pendulous position of the 

 stomach or proboscis when seen in profile (Plate I. Fig. 1), which neither enjoys the 

 great power of extension and contraction which characterizes Sarsia, nor is reduced to 

 the small size peculiar to Staurophora, nor so pressed against the upper disk as in 

 Tiaropsis. It is here a square mass, more or less star-shaped in its outline, when seen 

 from above (Plate I. Fig. 3, 4), or from below (Fig. 2) ; not longer than it is broad, but 

 which, morphologically speaking, answers strictly to the proboscis of Sarsia. The analogy 

 is the greater from the position of the sexual apparatus in the two genera ; eggs and sper- 

 matic cells arising in both only from the external walls of this central organ. The color 

 of the stomachal bulb, however, is very peculiar, inasmuch as in different individuals of 

 the same species it is either pale-yellow, or orange, or simply purple and brown ; no 

 doubt this coloration is owing to peculiar cells lining its inner surface, which may have 

 something to do with digestion, and perhaps may be analogous to hepatic cells, though 

 I have been unable to satisfy myself on this point. 



