Chap. III. GENUS BOLINA. 253 



tentacles are more and more developed in proportion as they are further removed 

 from the mouth. But Leucothea shows that oral tentacles may be as extensively 

 developed as those which issue from the sides of the Ijody. That the tentacles 

 of the Ctenophora? cannot be homologized with either the tentacles around the 

 mouth, or those around the disk, of Discoid Medusce, has already been shown. 



After this digression, if we return to a more direct consideration of the form 

 of Bolina, we find that it differs from Pleurobrachia in the extraordinary develop- 

 ment of two lobes in the actinal prolongation of the anterior and posterior sphero- 

 meres {Fi(/s. 88, and 89 s t n x), inclosing, when shut, the mouth and its appendages, 

 each lobe extending transversely to the antero-posterior diameter, one forward and 

 the other backward ; so that they contribute, when expanded, to increase the already 

 prominent length of the longitudinal diameter, leaving a deep, transverse chasm 

 between them, at the bottom and centre of which the mouth {Ficf. 88 m) is situated. 

 The 1jody thus shuts up by the alternate approximation and separation of two valve- 

 like lobes, hanging downward, and placed, one in front and the other behind the 

 spherosome, in a position precisely inverse to that of the A-alves of Acephala, which 

 rest upon the sides of the body, and move laterally. In addition to these two 

 large, broad lobes, there are on each side two smaller lobes (r r), the auricles, 

 which arise from the body at about the same height as the anterior and posterior 

 lobes. They are simple, short, narrow appendages, converging or diverging alter- 

 nately, and thus shutting from the side and above the great transverse fissure of 

 the animal. With the power which these animals enjoy of opening widely or 

 shutting closely the anterior and posterior lobes by contraction and dilatation, and 

 thus bringing them alternately close together or stretching them far forward and 

 backward, their general appearance is constantly so completely changing that it 

 requires a long acquaintance with them fully to appreciate the connection of all 

 their parts in their different attitudes, and the influence of the movements of certain 

 parts iq)on the position of others and upon their functions. The activity of the 

 circulation through the chymiferous tubes, and the jiosition the main l)ranches of 

 the central cavity assume during these changes, are constantly modified, as are also 

 the width of the body and the power of its contractions. And, in the same pro- 

 portion that the extent of the longitudinal diameter is modified by the expansion 

 and contraction of the anterior and posterior lobes, the height of the animal, com- 

 pared to its width and length, is also constantly changing. If we add to this 

 the diversity of images which are brought before us when we watch these animals 

 in their various movements from different sides, facing alternately the longer or 

 the shorter diameter, the sides or the actinal and the abactinal areas, I venture 

 to say, that it is impossible to make correct descriptions and to give true rep- 

 resentations of such animals, unless they have been watched for a long time in 



