Chap. IH. GENUS BOLINA. 265 



which the tentacles may be withdrawn, but simply two narroAv tubes arising close 

 together from the main chymiferous cavity, a little outside of the tubes of the 

 digestive cavity, and following the course of the latter to the tentacular bulb. As, 

 on account of the lateral compression of the body, the tubes of the digestive cavity 

 and those of the tentacidar bulb are brought into close proximity, they appear, at 

 first sight, to constitute a single cord on each side ; but in reality that 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 immediately upon the digestive cavity and extending to the margin 

 of the mouth. But whenever, by an oblique movement of the margins of the mouth, 

 or by the dilatation of the digestive sac one way or the other, the coeliac tube 

 is moved out of its vertical course, the relative position of the bulb of the ten- 

 tacular tube with reference to the coeliac tul:)e is changed, it may be seen how 

 the tube following the walls of the digestive cavity divides into two horizontal 

 branches, extending in opposite directions along the lateral margins of the mouth, 

 forward and backward, at right angles with the tube from which they arise. As 

 these branches meet the actinal prolongations of the lateral ambulacra, a direct 

 communication is established between the peripheric course of the ambulacral tubes 

 and the main chymiferous cavity, and this anastomosis very likely gives passage 

 to so much of the circulating fluid as does not return through the same tubes 

 through which it is propelled from the main trunks of the chymiferous system. 

 As for the two small tubes which extend to the bulb of the tentacles, they arise 

 from the same lateral bulging of the main chymiferous cavity from which the lateral 

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



The greater simplicity of the tentacular bulb of Bolina, when compared to the 

 large socket and complicated tentacular apparatus of Pleurobrachia, 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 forward and backward along that margin, forming, when con- 

 tracted, a compact bunch, and appearing, when expanded, like a disorderly brush 

 of irregularly curled threads tied together on one side. 



The best attitude in which to study the ramifications of the coeliac tubes on 

 the side of the digestive cavity, or rather along the outer margin of the mouth, 

 and to ascertain their position with reference to the tentacular bulb, which lies 

 farther outward, is when the animal is turned mouth upward with its large lobes 

 fully expanded. The mouth then appears like a narrow rim in the centre of the 

 prominent gelatinous mass, encircled by large lobes, which constitutes a sort of 

 compressed isthmus trending backward and forward on the actinal side of the body, 



VOL. III. 34 



