TYPE PR080P70IA. 



265 



This vestibule is a deep depression of the oral surface of the 

 larva, differing from that of the Pedicellina larva only in hav- 

 ing an arch-like thickening of its walls (only one side of the 

 arch is represented in the figure) which imperfectly separates 

 an oral portion of the vestibule from a posterior or anal 

 portion, a glandular depression situated in the roof of this 

 latter portion constituting the adhesive organ {ad). In front 

 of the oral vestibule is situated a ciliated depression from 

 which projects a tuft of long cilia and which appears to 

 correspond to the cement-gland of the Pedicellina larva and 

 to a glandular structure in the more modified Ectoprocta 

 larvae, known as the pyriform organ (pyr), by which name it 

 may be known here. The similarity of this larva to that of 

 Fedicellina is clear, the details of organization of the two forms 

 agreeing part for part ; in other Ectoprocta, however, great 

 differences are to be found. In the genus Bugula, for exam- 

 ple, the larva (Fig. 118) is a barrel-shaped organism at the one 

 extremity of which is a thickening, 

 the calotte {cal), which appears to 

 correspond, in part at any rate, to 

 the apical thickening or dorsal organ, 

 as it is sometimes termed, of Pedicel- 

 lina and Gyphonautes. The sides of 

 the barrel are formed by a circle 

 of elongated cells forming the corona 

 and equivalent to the marginal 

 corona of the other larvse ; it does 

 not, however, form a simple band in 

 Bugula, but its cells are much 

 shorter on one of the faces of the 

 embryo than elsewhere, producing 



a well-marked groove at the apex of which lies the pyriform 

 organ {pyr) whose homologies in Gyphonautes have already 

 been pointed out. A peculiarity of this larva is the entire 

 absence of a digestive tract, the lower end of the barrel being 

 occupied by a depression, the adhesive organ {ad). 



Between such a larva as that just described, entirely des- 

 titute of a digestive tract, and that of Gyphonautes intermediate 

 stages occur, as for instance in the larvse of the Cyclostomata, 



acl 

 Fig. 118.— Lakva of 



flabelUUa (after Babeois). 

 Letters as in Kg. 117. 



