162 SIDNEY ¥. HAEMEE. 



to prove that the lophophore itself is developed from a mor- 

 phologically prseoral portion of the oral groove. 



The relation between the velum proper and the oral cilia has 

 become, in the Eatoprocta, considerably complicated by the 

 formation of a fold of integument (vestibular wall), carrying 

 the former to some distance from the latter. When the 

 Pedicellina larva attaches itself, the distance between the two 

 structures becomes increased. TJie velar portion maintains its 

 position at fixation, and soon atrophies ; the oral groove, on 

 the contrary, growing away from the degenerated velum. Even 

 during the phylogenetic history of the process we may suppose 

 that the velum atrophied at fixation. This is par excellence 

 a locomotive structure, and vrould be useless in an attached 

 condition. The oral cilia would, however, continue (in the 

 hypothetical stage of fig. 18) to convey food to the mouth, and 

 the cells bearing them would, after a time, hecome prolonged 

 into tentacles, by which their range of activity would be 

 extended. 



During the abbreviated metamorphosis of Pedicellina it 

 has hence resulted (if the above be true) that the velum takes 

 no part in the change of position involved in the passage to the 

 adult condition. 



Summarizing the above, I may express my conviction (1) 

 that the metamorphosis of Pedicellina is a simple modifica- 

 tion of a more archaic process, due to abbreviation of develop- 

 ment, (2) that the oral groove persists in part as the adult 

 lophophore, (3) that the vestibule closes at fixation, and under- 

 goes the whole of its alterations in the interior of the larva, 

 opening secondarily only when the adult condition is practi- 

 cally attained. 



The adult form is reached by the elongation of the stalk of 

 fig. 10, and by the replacement of its contained " globules " by 

 characteristic connective-tissue and muscle-cells ; by the for- 

 mation of a stolon and a diaphragm, and by various alterations 

 in the calyx. The more important of these consist in the 

 complete (or almost complete) loss of the obliquity of the 

 lophophore, in the development of the permanent ganglion 



