vin] SOME STRUCTURAL FEATURES 111 



the "needles " slide to and fro : the edges of the groo ve 

 are turned in so as to form long slots in which the 

 outer ridges of the needles, right and left, are lodged. 

 The "needles" can thus slide freely forwards and 

 backwards within the "director," but cannot easily 

 be separated from it nor drop out of their respective 

 slots. The whole may be compared to an inverted 

 gutter-pipe, whose sides have been pinched together 

 towards the hinder end, and whose edges have been 

 fitted with a turned-in flange partly enclosing the 

 concavity and lodging two rods within it (vide figs. 

 18, 19). 



At its front end the "director" is enlarged, and its 

 groove widens out: in this region the "needles" be- 

 come free from the inturned flange, but they are still 

 kept in contact and parallel with the margin of the 

 "director" by a double series of peculiar hairs, about 

 fifty in number, situated on its inner face near the 

 lower edge on each side. The outer edge of the 

 "needle" runs between the upper and lower series 

 of hairs, and is thus retained in position. Within 

 the tapering hinder part of the director these hairs 

 are replaced by studs, which cluster in a group in 

 the anterior portion, but are isolated and rather 

 irregularly disposed in the narrower posterior region. 

 These studs prevent any displacement of the "needles " 

 in the passage through the director. Forwards the 

 "needles" diverge from one another and bend rather 



