322 MR FRANK BALFOUR-BROWNE ON 



Segment 8 is represented by a partially chitinised tergite, immediately underneath 

 which opens the anus. On either side of this tergite (8'), extending round the sides 

 of the segment, is a narrow chitinous band (y). The two bands extend to the ventral 

 face of the segment and then turn through about a right angle and pass backward, 

 lying more or less parallel to one another. These chitinised bands do not seem to 

 represent any regular sclerite of the segment, but are rather a specialised carrier 

 for the sexual armature which is pivoted on the apices of the two parallel ventral 

 chitinous rods (xx). 



The bands are, however, undoubtedly part of the 8th segment, and the part which, 

 in Hydrophilus, Peytoureau regards as the 8th tergite (c), is situated posteriorly 

 with regard to them. 



The sexual armature consists of two swollen masses (aa) from the upper side of each 

 of which a long tapering filament (bb) about 1 mm. in length projects backwards. 

 These two filaments, which correspond with Peytoureau's " deux autres apophyses 

 laterales plus longues . . .", are the spinnerets, and consist each of three portions, a 

 long basal segment and a short apical one bearing a long fine and tapering hair. On the 

 ventral side of the armature, between the swollen bases of the spinnerets, projects a thin 

 chitinised membrane (c) — (which, from Peytoureau's drawing (plate xx. fig. 3, viii.), I 

 gather he regards as the sternite of the segment) — which, in a ventral view, has a deep 

 groove running up its median line on either side of which the membrane fits round the 

 base of a spinneret, the middle region of the posterior free margin projecting into 

 two horn-like processes between the spinnerets and one on either side of the median 

 groove. The posterior free edge of this membrane is fringed with hairs and the two 

 horn-like processes are Peytoureau's " deux apophyses, simples, courtes dirige'es en 

 arriere," etc. 



The vagina opens between the spinnerets and just dorsal to this ventral chitinous 

 plate, so that if Peytoureau is correct in describing this ventral plate as the 8th sternite, 

 the genital aperture is, on his own showing, not between the 7th and 8th segments, but 

 posterior to the 8th. 



I have said that the armature is pivoted on the two chitinous rods (xx) previously 

 described. When the genital armature is in a state of rest, the swollen bases of the 

 spinnerets are drawn back by muscles attached to them dorsally, by reason of which 

 they turn on the two pivots already referred to, and under these circumstances the 

 spinnerets are concealed for about half their length by the grooved ventral plate which 

 wraps round them, since the ventral plate is fixed and does not move on the pivots 

 (vide fig. 14). When the armature is in a position of activity the bases of the spinnerets 

 are thrown forward on the pivots and the spinnerets thus project farther beyond the 

 grooved ventral plate. The pivots upon which the spinnerets swing are apparently 

 what Peytoureau describes as " l'articulation tergo-sternale du huitieme urite. . . ." 

 Peytoureau's figure (plate xx. fig. 1) represents what appears to me to be a dis- 

 section of the parts in a state of rest. 



