32 MARINE ANIMALS OF MASSACHUSETTS BAY. 



examination shows that the circulating tubes connected with the 

 longer row extend into the lobes, where they wind about in a 

 variety of complicated involutions. (Fig. 32.) The movements 

 of the Bolina are more sluggish than those of the Pleurobrachia, 

 and the long tentacles, so graceful an ornament to the latter, are 

 wanting in the former. With these exceptions the description 

 given above of the Pleurobrachia will serve equally well for the 

 Bolina. The structure is the same in all essential points, though 

 it differs in the size and proportion of certain external features, 

 and its play of color is less brilliant than that of the Pleuro- 

 brachia. The Bolina, with its slow, undulating motion, its broad 

 lobes sometimes spreading widely, at other times folded over the 

 mouth, its delicacy of tint and texture, and its rows of vibrating 

 fringes along the surface, is nevertheless a very beautiful object, 

 and well rewards the extreme care without which it dies at once 

 in confinement. 



Idyid. (Idyia. roseola AG.) 



The lowest genus of Ctenophora3 found on our coast, the Idyia 

 (Fig. 33), has neither the tentacles of the Pleurobrachia, nor the 

 lobes of the Bolina. It is a simple ovate sphere, the interior of 

 which is almost entirely occupied by an immense digestive cavity. 

 It would seem that the reception and digestion of food is intended 

 rig 33 to be the almost exclusive function of this 



animal, for it has a mouth whose ample di- 

 mensions correspond with its capacious stom- 

 ach. Instead of the longitudinal split serving 

 as a mouth, in the Bolina and Pleurobrachia, 

 one end of the body in the Idyia is completely 

 open (Fig. 33), so that occasionally some un- 

 suspicious victim of smaller diameter than 

 itself may be seen to swim into this wide por- 

 tal, when suddenly the door closes behind him 

 with a quick contraction, and he finds himself a prisoner. The 

 Idyia does not always obtain its food after this indolent fashion 



Fig. 33 Idyia roseola seen from the broad side, half natural size ; a anal opening, b lateral tube, c 

 circular tube, d efg h rows of locomotive flappers. (Agassiz.) 



