TENTACULA EESPIEATOEY OEGANS. 



443 



Fig. 230. 



double sheath protecting the setae. The whole apparatus, observes 

 Professor Williamson, is very similar to that seen in the tentacles of the 

 Snail, and appears to constitute rather a tactile than a respiratory organ. 

 This is rendered the more probable by the fact that, when the animal 

 first emerges from its tessellated case, the extremities of these two ten- 

 tacles are the first parts to make their appearance, the two curved 

 hooks, named by Schaffer the lips (fig. 227, 1, 6), being the next. The 

 setae are usually half drawn into the inverted tentacle, but they project 

 suflieiently forward to constitute delicate organs of touch, supposing the 

 deltoid body, into which they 

 are implanted, to be endowed 

 with sensibility. The animal 

 cautiously protrudes these 

 tentacles before it ventures to 

 unfold its rotatory organs ; but 

 it does not direct them from 

 side to side, as an insect does 

 its antennae. 



(1147.) In addition to the 

 elaborate organization de- 

 scribed above, the Prussian 

 naturalist conceived that he 

 had discovered a. vascular 

 apparatus, consisting of trans- 

 verse vessels (fig. 230, n n), 

 in which he supposed a cir- 

 culation of the nutritive fluids 

 occurred. But the vascular 

 character of the transverse 

 striae visible in this position 

 is more than doubtful, as there 

 seems every reason to suppose 

 that the appearance depicted 

 in the figure is due to the 

 existence of the transverse 

 muscular bands whereby the 

 extrusion of the rotatory apparatus is effected, analogous to those occu- 

 pying a similar situation in the Bryozoa. 



1148.) The mode in which respiration is effected, in the class of 

 animals under consideration, has been a subject of much dispute. Some 

 have supposed the contact of water, applied to the general surface of the 

 body, sufficient for the aeration of the nutritious juices, especially as its 

 constant renewal would be ensured by the ciliary movements. Bory St. 

 Vincent*, on the contrary, regarded the rotatory cilia as real gills, re- 

 * Diet, des Sci. Nat., art. " EOTIFERA." 



Notommata clavulata (after Ehrenberg) : a, rota- 

 tory organs; b, gizzard; c, stomach; d d, intestine ; 

 e, caecal appendages to stomach ; f, ovary ; g, con- 

 tractile vesicle ; h h, lateral tubes, to which are ap- 

 pended the vibratory organs ; n n, transverse bands, 

 supposed byEhrenbergto belong to a vascular system. 



