254 CONTRIBUTIONS TO THK NATURAL HISTORY 



Geryonidas, Oceanidae, iEquoridse, Beienicidae, which constitute his natural group of Dis- 

 cophorse cryptocarpae, answering closely to that of Forhes's naked-eyed Medusae, — it is 

 now obvious that Eschscholtz's division of Discophorae cryptocarpae rests upon the igno- 

 rance of tlieir true mode of reproduction, rather than upon any fundamental common char- 

 acter; and though he alludes to the absence of what he calls the eight marginal granules, 

 which we now call eye-specks, and which are known to exist also, but in another form, 

 in the naked-eyed Medusae, still this division rests altogether upon an imperfect knowl- 

 edge of these animals. Lesson himself, though his work is published at a period when 

 so many facts had been ascertained respecting the structure of Medusae, did not rec- 

 ognize the common structure of this type, and subdivides it into various families without 

 a common character. 



The characters common to all naked-eyed Medusae consist, in the first place, in the 

 general character which they have in common with all other Discophorae, to which great 

 order of Medusae they belong, implying the existence of a gelatinous disk, and a central 

 digestive apparatus. In the naked-eyed Medusae, this gelatinous disk is generally more 

 hemispherical, and less flattened than in the larger Medusae with protected eyes ; also, 

 as far as I can ascertain, all naked-eyed Medusae have a continuous circular tube, into 

 Avhich open the few radiating vessels which arise from the central cavity of the digestive 

 system. It is true, in the common Discophorae, there is also a marginal connection of 

 the radiating branches of the chymiferous system. But there it is rather an anastomosis 

 of minute vessels, while here we have a regular circular tube, in which fluids move to and 

 fro, and into which the radiating tubes open largely. This circular tube forms so prom- 

 inent a feature in the structure of the naked-eyed Medusae, that it marks out the lower or 

 peripheric margin of the animal, and that the eye-specks, tentacles, and all the various 

 ornaments of the margin of the disk seem to be connected with it, or to arise from it, or 

 to be more or less dependent upon it; and, indeed, from the large supply of nourish- 

 ment constantly circulating in the circular tube, I have no doubt that the life of the 

 parts surrounding it is more active and intense than that of any other part of the body, 

 owing to the regular, fresh supply they receive from the digestive cavity. The main cord 

 of the nervous system itself is connected with this circular tube, and follows it on its inner 

 margin all round. Muscles in vertical bundles outside and inside of the gelatinous disk 

 regulate the locomotion, assisted by a system of circular fibres upon the inner cavity, and 

 another within the partition, which stretches more or less extensively from the lower mar- 

 gin inwards. Tentacles, varying extraordinarily in number and size and arrangement, 

 arise from this same lower margin, and the eye-specks themselves are placed in the same 

 position, either between the tentacles, or upon their base, or their inner or outer surface. 



