104 



ZYGODACTYLA GROENLANDICA. 



the bulging part of the spherosome, the free space left in the centre 

 F!c 163. having a radius of about 



one third that of the 

 spherosome itself The 

 lips of the actinostome 

 are formed by the foldmg 

 of the membrane of the 

 digestive cavity along the 

 direction of the radius ; 

 as the membrane becomes 

 more and more fimbri- 

 ated, the fold becomes 

 deeper and deeper, and 

 projects beyond the gen- 

 eral outline, like an ex- 

 ceedingly delicate frill. 

 The tentacles at the base 

 are swollen, taper very 

 suddenly, are hollow (Fig. 155), the walls of the tentacles are thin, 

 and the lasso cells are arranged irregularly over the whole surface in 

 small clusters. At the base rig. ist. 



of each of the large tentacles 

 there is a small hollow spur 

 (s. Fig. 155) projecting inward, 

 the walls of which are thick, 

 and made up of large cells ; 

 the rudimentary tentacles are 

 swollen at the extremity, and 

 the spur is not develoj^ed until 

 the lash of the tentacle be- 

 comes apparent ; the marginal capsules are large, ellipsoid, with two 

 large granules in each. In young specimens of Zygodactyla, not hav- 

 ing more than forty large chymif- 

 erous tubes reaching to the mar- 

 gin, we find the other tubes but 

 slightly developed, two or three 

 sometimes between each of the 

 larger tubes extending from the 

 upper edge of the digestive cav- 

 ity to various distances from it ; 



rig. 153. Abactlnal view of Zygodactyla groenlandlca. 

 Fig. 154. Profile view of Fig. 153, lialf natural size. 



Fig. 155. Portion of the circular tube, showing the mode of development of the marginal ten- 

 tacles, .s, spur of marginal tentacles. 



