OF THE ACALEPHjE OF NORTH AMERICA. 363 



to constitute a single cord on eacli side ; but in reality tliat cord consists of three tubes 

 running in the same direction, which, being close together, are very easily mistaken 

 one for the other, and whose natural connections are still more difficult to ascertain, 

 as the bulb of the tentacle exactly covers the termination of the tube, resting im- 

 mediately upon the digestive cavity and extending to the margin of the mouth. But 

 whenever, by an oblique movement of the margin of the mouth, or by the dilatation of 

 the tube, one way or the other, out of the vertical direction, the superposition of the bulb 

 of the stomachal tube is disturbed, it must be seen how the tube of the digestive cavity 

 divides into two horizontal branches, extending in opposite directions along the lateral 

 margin of the mouth forwards and backwards, at right angles with the tube from which 

 they arise, so that a direct communication is here established between the peripheric 

 course of the ambulacral tubes and the main central cavity, a communication which 

 very likely gives passage to the recurrent fluid, which does not return through the 

 same tubes in its course. As for the two small tubes which unite in the bulb of the 

 tentacles, they arise from the same lateral bulging of the same cavity from which the 

 lateral tube of the stomach originates, but they arise more vertically. 



The greater simplicity of the tentacular bulb has reference, no doubt, to the shortness 

 of the tentacles, and to the circumstance that they are not protruded to any length 

 beyond the margin of the mouth, but simply extend in a winding course forwards and 

 backwards along that margin, forming, when contracted, a compact bunch, and appear- 

 ing, when expanded, like a disorderly brush of irregular curled threads tied together 

 on one side. 



The best position in which to study the ramifications of the tubes on the side of 

 the digestive cavity along the outer margin of the mouth, and the position of the ten- 

 tacular bulb still farther outward, is when the animal is turned mouth upwards, with 

 its large lobes fully expanded, when the mouth appears like a narrow rim in the centre 

 of the prominent gelatinous mass between the large lobes which constitute a sort of 

 compressed isthmus between the antero-posterior extremity of the body, along the margin 

 of which the horizontal tubes from the stomachal tube arc seen to extend as far as the 

 right margin of the lateral auricles, without entering into direct communication with' 

 the tubes of the tentacular bulb. See Plate VIII. Fig. 6. 



The walls of the central chymiferous cavity, and the main trunks which arise from 

 it, are distinctly fibrous, and may easily be seen to shorten or elongate, and enlarge 

 or contract their cavity. 



The funnel enlarges above into two distinct branches, forming two bulbs, as in Pleu- 

 robrachia, with oblique openings forwards and backwards, on the sides of the circum- 



