CYANEA AUEITA. 109 



ments, the structure of which is by no means so simple as has been 

 generally imagined. The exterior of these tegumentary membranes, 

 covering the convex surface of the disk, consists of a dense tissue made 

 up of hexagonal cells containing a soft whitish substance mixed up 

 with little granules, and presents upon its outer surface innumerable 

 little suckers or agglomerations of granular bodies, which are visible to 

 the naked eye. 



(278.) The concave or ventral surface of the disk is furnished with a 

 double investment, consisting of an outer and inner layer, the external 

 of which resembles in its structure the dorsal membrane described 

 above, and constitutes a sort of epidermic covering. The inner layer, 

 which in its intimate texture likewise consists of hexagonal cells, 

 encloses nothing but a number of isolated granules, clear and translu- 

 cent as water. The interspace between this inner layer and the 

 dorsal integument is considerably greater than that which separates it 

 from the ventral surface ; both these spaces, however, are filled up with 

 a clear gelatinous mass, wherein are distinguishable numerous isolated 

 granular bodies, of a rounded shape and of unequal size, that seem to 

 be all connected with each other by fibres or extremely delicate vessels, 

 and not supported by expansions of cellular membrane. The rest of 

 the gelatinous mass is too transparent to allow any organization to be 

 detected ; this, however, is in small proportion, and encloses the large 

 vessels belonging to the nutritive apparatus, immediately to be described. 



(279.) The opening of the mouth is situated in the centre of the 

 lower surface of the disk, between the four arms suspended from that 

 portion of the body. The mouth itself consists of a short quadrangular 

 tube, from the angles of which the arms are dependent. Each arm is 

 composed of a thick central cartilage, whereunto are attached two 

 membranous laminae, variously plaited and puckered throughout their 

 entire length, and moreover at certain seasons gathered into little 

 pouches or pockets, to be hereafter mentioned in connexion with the 

 generative apparatus. 



(280.) Superiorly the oral aperture terminates in four short tubes 

 arising from its four angles; and these, diverging, mount upwards, 

 supported by a cartilaginous prolongation derived from the central 

 supports of the arms. These four tubes evidently represent the oeso- 

 phagus and lead into four ample stomachs of a subglobular shape, 

 which are smooth internally and lined by a special membrane, wherein 

 may be seen numerous little granular bodies, but no vessels. 



(281.) From the above stomachal cavities proceed several large 

 canals that diverge towards the circumference of the disk, and consti- 

 tute a part of the digestive apparatus. One of these vessels arises 

 immediately from the dilated portion of each cesophageal tube ; and 

 these, dividing and subdividing dichotomously, ramify towards the 

 margin of the disk. From each of the four stomachs three other 



