26 



cells, end open oxtomally in fi'ont '•"f 1 ' '■« 'posterior ad- 

 ductor. The internal, pericardial openings I have not 

 been able to find. Lyinf; around the cerebral ^'••""' -lion is 

 a gland, wliich so far as known, is peculiar to " ip- 

 womis" and whicli in later stages, becomes so rroatly de- 

 veloped in connection with the gills. The glandular por- 

 tion (c;.!). , rig.2u) contains spherical cells, and from it 

 a duct opens to the exterior (d.D. ) under the cerebral 

 r:anrlion. 



»Metamorphosis. - The duration of the f ree-swimrning life 

 of th.olarva is not knovm, but it is perhaps a month, more 

 or Itss. In a very much shorter period, the peculiar 

 "Siiip-v/orm" has been developed, with adult organization. 

 The first change is the sudden, com];)lete loss of the velum. 

 V/ithin a few hours after the larva has settled, tlie veliom 

 begins to disintegrate, and its constituent cells are cast 

 off and eated by the larva. The lower lip is projected 

 forv/ards under the cavity of the veliun, and as the cells 

 are cast off, they cannot pass to the exterior, and 

 eaten. The basement membrane of the cells of the velum 

 contracts rapidly and the cavity of the velum is very 



