Chap. II. GRADATION AMONG ACALEPHS. 117 



highly organized e^^es, in definite number, and these eyes are always placed at 

 the marginal end of some specially organized radiating tube, alternating with other 

 tubes of a different character; thus exhibiting a higher complication of these parts, 

 not only in their structure, but also in the definiteness of their relations to one 

 another, in their alternation Avith one another, and in their numeric limitation. 

 Some Discophora^ have no other marginal organs besides eyes ; but there are those 

 that are provided with variously combined tentacles also : in none, however, are 

 the eye-specks connected with tentacles, though the eyes are themselves modified 

 tentacles. 



In the naked-e3'ed Medusa^, the ovaries and spermaries follow the track of the 

 radiating chymiferous tubes, and are variously circumscribed in their extent : in 

 some, they are limited to the walls of the proboscis, in others they extend all 

 along the chymiferous tubes proper, and in others they occupy only a part of the 

 course of these tubes ; but they are never circumscribed within distinct pouches, 

 as in the Discophoraj proper. In these, the ovaries and spermaries bear identical 

 homological relations to the chymiferous tubes, as far as their position is concerned ; 

 but, owing to their higher develojjment and to their isolation, they form distinct 

 bunches, hanging in distinct pouches on the lower side of the disk, and stand in 

 definite relations to the parts surrounding the actinostomo, through which the eggs 

 are laid, while in the naked-eyed Medusae the eggs simply drop from the ovary 

 into the water ^Aathout ever passing through the actinostome. Imperfect and 

 injured specimens may leave a different impression rcsj^ecting the mode of escape 

 of the eggs from the ovaries ; but I shall show hereafter that these egg pouches 

 are really closed, and do not naturally open outward, as Ehrenberg represents them, 

 but communicate only with the main cavity of the body, and through it with the 

 actinostome, through which the eggs or the young finally make their escape into 

 the water, after having remained for a longer or shorter time suspended in the 

 jieripheric folds of the actinostome. 



In Discophoraj proper, the actinostome is far more complicated than in the 

 naked-eyed MedusEe. In the latter, it is only a pi'ojecting fold of the lower wall 

 of the spherosome, either extending simply as a circular rim beyond the main 

 cavity, with or without fringes, or forming a more or less elongated proboscis. 

 In Discophorte proper, the actinostome is as it were suspended between distinct 

 pillars hanging from the spherosome, which expand into more or less complicated 

 leafy folds, the edges of which are either free, as in Aurella, Pelagia, Cyanea, etc., 

 or partially soldered together, as in Rhizostoma, Polyclonia, etc., thus fornung either 

 open or partially closed channels leading from their peripheric termination to the 

 main cavity, which is itself wide and capacious, and supported laterally by the 

 pillars of the actinostome. The cavities formed by the leafy folds of the acti- 



