376 NATURAL HISTORY OF AQUATIC INSECTS CH. 



abdomen, as I learn from Mr. Hammond, which are 

 no doubt useful during prolonged submersion. The 

 eyes are very curious. A chitinous plate protects and 

 almost entirely covers them, leaving only a small 

 round central hole. The form of this plate suggests 

 that it may be employed as a kind of pin-hole 

 camera. Mr. Hammond, who called my attention 

 to this peculiarity, has drawn it in fig. 114. The 

 tibia of the fore leg is provided with a peculiar comb- 

 like organ (see fig. 116), which 

 looks as if it might be useful for 

 cleaning the antenna; or limbs. 

 Such an apparatus is not uncom- 

 mon in Beetles. I am indebted 

 to Mr. W. F. Baker for the fol- 

 lowing remarks upon the tibial 

 comb : — • 



" If the fore leg of the common 

 Beetle, Pterostichus niger, be ex- 

 amined closely, a deep notch pro- 

 tected b}' a large spine will be 

 found on the lower side of the 

 tibia ; this notch is armed with 

 stiff, fine hairs. I was for a long 

 timic unable to imagine what pur- 

 pose it could serve. After inspect- 

 incr all the Beetles in mv collec- 

 tion, I found that this peculiar 

 feature was restricted to the Geo- 

 dephaga, though in some of the 

 Staphylinidse a somewhat similar structure, consist- 

 ing of a spine and fine hairs without any notch, could 



Fig. 114. — Eyeof Aepus. 

 A, External surface 

 showirij; facets. B, 

 Perfofd ted plate, front 

 view. C, sectijii. 



