OF THE ACALEPHiE OF NORTH AMERICA. 273 



to justify the opinion that the dark-colored specks at the base of the tentacles are con- 

 nected with the faculty which these animals distinctly possess of distinguishing light from 

 darkness, although the connection with the nervous ganglia may not be such as to allow 

 the formation of a distinct visual image. 



The connection of the tentacles and eye-specks is closer in this animal than it is in 

 any other of the naked-eyed Medusae, with the exception, perhaps, of Sarsia and Slab- 

 beria, in which the eye-specks rest also upon the base of the tentacles. In Sarsia, how- 

 ever, the eye-speck is on the upper side of the tentacles, and the whole bud is 

 less connected with them than it is in Hippocrene. Moreover, the tentacles being 

 hollow in Sarsia, and in direct communication with the chymiferous tube, they must at 

 once appear in closer connection with the chymiferous system than with the eye-specks; 

 while in Hippocrene the tentacles, being excluded from any connection with the chymif- 

 erous system, appear connected only with the sensitive buds ; so that the relations of the 

 apparatus are considerably modified in the two types ; and the fact that in Hippocrene so 

 many eye-specks are combined in so close a manner into one and the same bud, with as 

 many tentacles, introduces here a relation of the tentacles which is peculiar, and doubt- 

 less has reference also to their peculiar structure, in which nettling cells are so few, if, 

 indeed, there be any proper nettling cells. 



The name super ciliaris, applied to this species, is derived from this connection of the 

 tentacles with the eye-specks. Although this peculiarity is generic, it may be said that, 

 in Bougainvillia nigritella of Forbes, there is but one tentacle to each bud, if the specimens 

 observed were at all perfect; that there are fewer in Bougainvillia Britannica than in the 

 North American species ; and that in the original species, as described by Lesson, there 

 are also fewer ; so that the name of Hippocrene superciliaris appears quite appropriate for 

 this species. 



The above details, respecting the sensitive apparatus of so small an animal as this, will 

 further justify the general remark already made, that there is here a much closer connec- 

 tion between the structure and form than is observed in any other type of the animal king- 

 dom. Indeed, the bulbs at the four corners of the lower margin, with their movable ap- 

 pendages, form so prominent a feature in the appearance of these little animals, that at first 

 sight nothing in them strikes the eye but those four dark prominences, with the main central 

 digestive cavity ; and whenever an attempt at a minute description is made, even if it be 

 restricted to external appearances of form and color, it must include particulars which 

 have as much reference to the anatomical structure of these animals as to their external 

 appearance. 



As in all the other Medusae, in order to study well the arrangement of the muscular 



