100 CLASS III. 



observer, Dr F. WILL, found these threads in Eucharis (amongst 

 the Beroecea) without perceiving any irritation on touching it. 



In many there is only a single oral aperture, placed in the center 

 on the inferior surface of the body. In others many suctorial tentacles 

 are seen, or the arms have apertures conducting to tubes, which, 

 like vessels, fall into larger stems and finally open into a common 

 cavity, the stomach (Rhizostoma Cuv.). From the stomach arise 

 water-canals, which are provided internally with cilia. By some 

 writers these have been regarded as blood-vessels : but far rather 

 ought they to be considered as respiratory organs, since in part they 

 open freely on the surface of the body. But, in addition, blood- 

 vessels have been found, which, at least in Beroe 1 , lie round about 

 the water-canals, surrounding them like a sheath. Here nucleated 

 corpuscles have been observed (blood-corpuscles'?) which however 

 move only very slowly and irregularly. 



The sexual organs are distinct in the disciform Acalephes, but 

 have in both sexes the same form. In ^Equorea they lie in form of 

 folded plates on each side of the water-canals which spring from the 

 stomach, towards the inferior surface of the disc. In the eared 

 Medusa (Aurelia or Medusa aurita) there are four cavities, opening 

 below at the disc and which have been taken for respiratory cavi- 

 ties, in which lies a folded organ, that is, an ovary or a testis, 

 according as it contains ova or spermatozoa ; in most Acalephes the 

 spermatozoa have the ordinary cercarial form. In other Acalephes, 

 as Beroe, ovaries and testes are united in the same individual: 

 here they lie along what are called the ribs, beneath the skin. 



The metamorphoses, of which we have already spoken above, 

 are remarkable in young Medusce. The eggs, that pass from the 

 ovaries along the canal of the arms to their folds, are collected here 

 and carried about, for a time, by the mother in saccules which 

 afterwards disappear 2 . The young animals quit these receptacles 

 in the form of ciliated Infusories resembling Leucophrys or Bursaria. 

 These swim freely about, but after a short time (two or three days 

 according to SIEBOLD) become fixed by their thicker anterior ex- 

 tremity which has a sucker. Next, the body becomes cylindrical, 

 transparent, and at the free end, which thickens, an oral aperture is 



1 [The blood-vessels described by WILL could not be seen by FORBES, HUXLEY, 

 LEUCKART, &c.] 



2 See the figures of EHRENBERG Die Alcalephen &c. Tab. m. fig. i. 2. Tab. vm. fig. i. 



