Naked- Eyed Med usee or Jelly Fishes. 87 



of the disk, and through them passes into the circular tubes 

 around the lower margin." Professor Agassiz observes, 

 that while the circulation is properly a chyme circulation in 

 these animals, it is a chyle circulation in Articulata and 

 Mollusca, and in Vertebrata alone, true blood. The particles 

 in the circulating fluid of these Medusae are very irregular in 

 size and colour, and are evidently only the imperfectly digest- 

 ed food. 



The nervous cord, as distinctly made out by Professor 

 Agassiz, follows the circular submarginal tube on its inner 

 side, and like that, is a complete ring. At the base of the 

 cluster of marginal tentacles there is an enlargement or bulb- 

 like prominence. Each tentacle contains within its base a 

 black point which subserves the purpose of vision. The bulb 

 is not hollow in the Hippocrene, but contains an enlargement 

 of the nervous cord, which, as our author shews, may be con- 

 sidered a ganglion, although not purely nervous matter in its 

 constitution, and this position of the ganglion has a direct 

 relation to the organs of sense clustered near it. The nervous 

 cord, under a high magnifier, appeared as a string of several 

 rows of nucleated ovate cells ranging in irregular lines, the 

 cells not strictly in juxta-position by their ends, but alternate 

 more or less so as to form a cord-like mass ; and it was dis- 

 tincly observed passing into the angles of the sensitive bulbs. 

 The dark spot of the bulb consists of pigment cells, which 

 point to the centre of minute black eye-specks, shewing a close 

 connexion between the dark spots and the centre of the bulb 

 where the nervous ganglion is seated ; " and though this is 

 not an arrangement known in the organs of vision of any 

 other animals, we are at least reminded by those peculiari- 

 ties of the structure of the compound eye of insects, in which 

 the pigment pillars intervening between the nervous mass at 

 the base of the eyes present a structure not very different 

 from that of the radiating cones in the bulb of the Hippo- 

 crene." 



There is a similar ganglion in each of the four bulbs — 

 a branch of the nervous thread, or what appeared to be a 

 continuation of it, was detected along each chymiferous tube 

 leading upward towards the digestive cavity ; .and above. 



