124 



HYDROZOA. 



Fig. 60. 



length of the animal, passes transversely across the body in a straight 

 line from one side to the other, as represented in the engraving ; but 

 the details of its structure, and the nature of the vessels arising from 

 it, will be best understood by a reference to the enlarged diagram of 

 these parts given in the next figure (fig. 60). The mouth, i, is a rhom- 

 boidal depression, seen near the centre of the body, between the two 

 lateral rows of locomotive cilia, which extend from one end of the animal 

 to the other. From the mouth arise two tubes, j j, which terminate 

 in a globular cavity common to both (these would seem to constitute 

 the digestive apparatus) ; and a straight narrow tube, o, prolonged to 

 the opposite margin of the body to that which 

 the mouth occupies, may be regarded as an 

 intestine through which the residue of di- 

 gestion is discharged. From around the oral 

 extremity of the stomach, and from the glo- 

 bular cavity in which the two principal canals 

 terminate, arise vessels, t 1 1, which diverge 

 so as to form a cone, at the base of which 

 they all empty themselves into two circular 

 canals, one surrounding the mouth, and the 

 other encircling the anal aperture, which 

 precisely correspond with the vascular rings 

 already described in the JSeroe; and, from 

 these, four long vessels, or branchial arteries 

 as they might be termed, p p, q q, are pro- 

 longed beneath the four ciliated margins all 

 around the body. But besides these four 

 nutritive vessels, two others, x x, arise from 



^fCAWAV^ 



the anal ring, which run inwards towards Alimentary apparatus of ce*tum. 

 the centre of the animal, and afterwards 



assuming a longitudinal direction, serve to distribute nourishment to 

 the median portions of the animal. The casca, or blind tubes, n n, 

 appended to the intestine, may possibly furnish some secretion useful 

 in digestion, although perhaps we are scarcely warranted in saying 

 decidedly that they are biliary organs*. 



(324.) Extraordinary as must appear the powers which the AcalephaD 

 possess of seizing and dissolving other creatures apparently so dispro- 

 portioned to their strength and the delicate tissues which compose 

 their substance, there are other circumstances of their history equally 

 remarkable, which, in the present state of our knowledge, are still more 

 inexplicable. If a living Medusa be placed in a large vessel of fresh 

 sea-water, it will be found to secrete an abundant quantity of glairy 

 matter, which, exuding from the surface of its body, becomes diffused 



* Delle Chiaje, Memorie per servire alia storia degli Animali scnza Vertebre del 

 regno di Napoli. 4to, 1 823- 1 825. 



