TYPE PROSOPYGIA. 



263 



phic form is known as the Vibracula, and consists of a slender 

 filament movably articulated to a rounded structure corre- 

 sponding to the head of the Avicularia ; the filaments wave 

 continually to and fro and are probably tactile in function. 

 In many forms, too, in the neighborhood of the mouths of the 

 ordinary individuals sac-like pouches occur, in which the 

 ova undergo their development. These structures, known as 

 ovicells (Fig. 116, <>c], or ocecia, have also been considered modi- 

 fied individuals, but seem rather to be organs of the ordinary 

 individuals, arising as a pouching of their walls. Finally, not 

 infrequently certain individuals relinquish their nutritive 



cal 



B 



FIG. 117. A, LAUVA OF Pedicellina (after HATSCHEK) ; B, Cyphonautes (after 



PROUHO). 



ad = adhesive urguii. s = stomach. 



cal calotte. sh = shell. 



cor = corona. pyr = pyriform organ. 



function and serve as root-like anchors or stem-like supports 

 for the entire colony. 



As regards the internal structure of the Gymnolaemata it 

 is unnecessary to add anything to what has already been 

 stated in describing the general characteristics of the order 

 Ectoprocta. 



Development of the Polyzoa. The larva of Pcdi'Uut,a (Fig. 

 117, A), which may be taken as a type of the Endoprocta, is a 

 somewhat dome-shaped organism, the summit of the dome 

 being occupied by an apical thickening (cal) bearing a tuft of 

 cilia, while at the margin there is a stout ciliary baud, the 



