DI8COPHORA. 535 



tubes open at their base into the stomach. At the free extremity, 

 the tube of each subdivides and ramifies like the roots of a plant ; 

 terminating in a number of small suckers, in the centre of each 

 of which there is a small pore. It has been shown, by placing 

 one of these animals in a coloured fluid, that solid particles, if 

 sufficiently minute, may enter these pores ; but this species must 

 either be nourished by extremely minute animalcules, or by im- 

 bibing the juices of other animals, upon which it fixes its suckers. 



1188. According to Ehrenberg, a nervous circle may be de- 

 tected surrounding the mouth in some animals of this group ; 

 and imother, connected with the first, running round the margin 

 of the disk. Upon this point, however, there is considerable 

 doubt. The animals of this group appear very little sensitive 

 to injurious impressions. They give no signs of feeling the 

 deepest and most extensive wounds of their surface ; and the 

 movements of contraction and dilatation have been seen in parts 

 of the disk almost separated from the rest, as well as in the 

 entire animals when nearly two-thirds of their bulk had been 

 lost by the draining of their fluids. In such instances, the move- 

 ments may be re-excited after they have ceased, by friction and 

 by punctures of the fibrous substance, just like those of the heart 

 and alimentary canal in the higher animals ; and they would 

 seem to be of an equally involuntary character. 



1189. Round the edge of the disk, however, we find a series 

 of curious bodies which have generally been regarded as organs 

 of vision and hearing. The supposed auditory organs, which 

 are situated in the bulbs at the base of the marginal tentacula, 

 are small vesicles containing one or more spherical or oval cal- 

 careous concretions. The ocelli, or supposed visual organs, con- 

 sist of small aggregations of pigment-cells, surrounding a small 

 crystalline refractive body, which is said to be of a silicious 

 nature. From the characters presented by these ocelli, the late 

 Professor Forbes proposed to divide the Medusae into two great 

 groups, which appear to correspond in a remarkable manner 

 with the peculiarities in the mode of development of the animals. 

 In one of these the ocelli are always placed in notches between 

 the marginal tentacles, and the membranes in their vicinity are 



