ON THE LIFE-HISTORY OF PEDIOELLINA. 253 



last portion is obviously represented in Pedicellinaby the 

 ciliated oral grooves, continuous, as in Polygordius, with 

 the mouth. The relations of these grooves during the meta- 

 morphosis appear to me to deserve further consideration. 



We have found that the median postanal portion of the 

 vestibule is continuous with the oral grooves, of which it may, 

 indeed, be said to form a part. Acccording to Hatschek 

 (1) it is, like other portions of the vestibule, lined by ciliated 

 cells. 



If we are justified in assuming that the oral groove — a part 

 of the typical Trochospheral ciliary apparatus — extends, poten- 

 tially at least, from the mouth completely round the vestibule 

 to the postanal region, it seems to me that considerable light 

 is thrown on the metamorphosis. The morphological position 

 of the oral groove will be in no way altered during the rotation 

 of the alimentary canal, and in fig. 16 it will continue to pass 

 from the mouth round the ab-anal side of the altered lateral 

 folds to the median post- anal portion of the vestibule, even 

 though it is no longer distinguishable in the persisting division 

 of the latter structure. In figs. 16 and 6 we observe, however, 

 the commencement of a separation of the oral groove into two 

 parts — one continuous with, and becoming indistinguishable 

 from, the " oral" section of the vestibule {v. or. in fig. 16), and 

 the other potentially passing from the free apex of the epistome 

 in fig. 16 to the end of the reference line m. v. in the same 

 figure. The position of this latter portion will be the median 

 line passing from a. v. v. to m. v. Owing to the fact that it 

 is situated behind the anal cone it is, of course, unpaired (cf. 

 fig. 5), and it appears to me that its situation may be very 

 fairly considered to be represented by the linear groove which 

 in fig. 11 has formed the permanent vestibular aperture. From 

 the margins of this groove are developed the tentacles, which, 

 if the above reasoning is legitimate, are formed from the region 

 of the oral groove. 



The fact that the tentacles of the adult lophophore of the 

 oral side are on the ab-anal side of the mouth appears to me 



