Ixxvi INTRODUCTION. 



mouth of the zooecium^ the mandible taking the place of 

 the operculum. Within the chamber occurs a small cir- 

 cular body, composed of distinct cells, which is connected 

 (in Bugiila flabellata*) with a cup-shaped organ, opening 

 out through the membrane of the aperture. From the 

 bottom of the cup rise a number of setai, which project 

 beyond the opening and constitute the tactile organ 

 before referred to f. The cellular body (Woodcut, fig. 

 xxxix,, c), in connexion with the setiferous cup, has been 

 regarded as a nervous ganglion (Busk, Smitt) ; the two 

 together constitute, according to Nitsche, the homologue 

 of the polypide, which is here reduced, in conformity with 

 the altered significance of the whole structure, into a 

 mere organ of touch. There can be little doubt, I think, 

 that the latter is the true vicAv ; at the same time it must 

 be regarded as probable that the rudimentary polypide 

 is furnished with its nerve-centre, by which the powerful 

 muscular apparatus J and the sensitive organ may be 

 supplied. Whether the cellular body constitutes the 

 ganglion, we are not at present in a position to decide. 

 The articulated avicularia are always attached to the wall 

 of the cell, and usually at a short distance from the ori- 

 fice ; they are confined (apparently) to a comparatively 

 small number of genera. 



Some further evidence of the morphological nature of 

 these curious appendages may be briefly noticed, (i.) In 



* According to Nitsche, " Ueb. die Morphologie der Bryozoen," Zeitsch. 

 f. wissensch. Zool. xxi. 4 Heft, p. 111. 



t According to Busk this organ is protruded by tbe mere throwing back 

 of the mandible. When the avicularium is opened, it stands out promi- 

 nently on the upper surface. 



I Tlie muscles are disposed in two sets — one for the opening and the 

 other for the closure of the mandible ; they are composed of transversely 

 striated fibres. 



