6o8 Till: SENSES AND SENSORY ORGAN*. 



mounted entire as a microscopical object, its form is more 

 complicated. Lee was, I believe, the first who accurately 

 described the form it assumes, but he regarded it as its natural 

 condition. 



The integument of the capitellum is soft, except in three 

 lines, two of which are prolongations of the anterior, and one 

 of the posterior, portion of the scape. When the capitellum 

 is shrivelled or compressed, these portions of the integument 

 become salient, and the proximal portion of the capitellum 

 becomes subpyramidal with three triangular faces. The distal 

 portion is then seen to be deeply grooved, so that it is divided 

 into a proximal and distal portion. This groove is not visible 

 in the fresh halter, but is very apparent in most preparations. 

 It forms a spiral and is the line of attachment for the septum. 

 The groove commences on the inferior surface, close to three or 

 four large bristles, and terminates at a point nearly in the 

 same line, but at a more distal part of the capitellum. It is 

 deepest at its commencement. 



A curved sheet of elongated cells extends from this groove 

 to the septum of the scape, and forms the septum of the 

 capitellum. One of the canals of the scape terminates on 

 either side of this septum ; and the two cavities into which it 

 divides the capitellum communicate at the free edge of the 

 septum, so that a current of fluid passing from one canal to 

 the other takes a spiral course in the capitellum. 



It is not easy to describe the exact course of the septum in 

 the capitellum, but it may be compared to a single turn of the 

 spiral septum of a cochlea. Its edges are seen in a com- 

 pressed halter as a figure of 8. Its proximal portion is 

 attached on either side to one of the ridges on the capitellum 

 proceeding from the anterior canal of the scape. It is sub- 

 triangular, and its plane is axial to the scape and capitellum ; 

 its distal part curves into a plane approximately transverse to 

 the axis of the scape, and is inserted into the spiral line 

 already described ; it presents a free edge where it terminates 

 in the vicinity of the three or four long setae, where the spiral 

 groove formed by its insertion is deepest. The relations of the 



