20 



BRYOZOA ECTOPROCTA. 



an ectodermal invagination, into a wide gastric cavity that ends 

 blindly. A comparison with the larvae of Tendra and of Cyplio- 

 nautes renders it probable that the part lying behind the aperture of 

 the sucker corresponds to the anal region. This distinctly developed 

 alimentary canal appears to be a vestigial organ, there being no- 

 indication that it 



K 



'mmm 



■o$:$^'^^§N^x\x\\s \ \ , iu f . 



\. 







Tn 



actually functions. 

 It degenerates in 

 the further course- 

 of larval life. 



The thickness 

 of the epithelium 

 Avhich lines the 

 mantle-cavity {}>) 

 is remarkable, and 

 contrasts with the 

 somewhat thin 

 ectodermal layer 

 of the retractile 

 disc. Closely con- 

 nected witli the 

 latter layer, in the 

 anterior part of 

 the larva, there is 

 a cell-mass (Fig. 

 7 B, (J) which 

 Harmer (No 13) 



regards as the 

 l:)rain. This author 



arisnig 



Fig. 1.—A, larva of Alcyonidium mytili (after J. Babrois). B, 

 longitudinal vertical section through the larva of Alcyonidium 

 (diagram constructed after the figures of Harmer). c, coronal 

 cells; g, brain (?) ; m, oral aperture; o, pyriforni organ; i>, 

 mantle-cavity; r, retractile disc; s, sucker. 



observed, 



within this cell-mass, fibrous strands, some of which are said to 

 become connected with cells of the ectodermal furrow, while others 

 can be followed into the neighbourhood of the large coronal cells. 

 Should these statements be confirmed, we should appear justified in 

 considering the pyriform organ as a sensory organ, Avhereas until now 

 its histological constitution seemed to point to the conclusion that it 

 functioned as a gland. The presence of a larval brain comparable in 

 position to the neural plate would be of importance in tracing the 

 Ectoproctous larvae back to the Troclioplwre. The statements of 

 Harmer have recently been confirmed by the researches of Prouhq 

 (Xo. 28) in connection with Flustrella, but on account of the 



