THE BOOK OF NATURE STUDY 



with which to maintain a grasp upon the female in the act of 

 mating. In this process the cups are flattened down upon the 



smooth surface of the prothorax 

 of the female, and from each there 

 exudes a sticky, coagulable fluid 

 which, passing down the stalk of 

 the cup, escapes by a minute hole, 

 which pierces the centre of the 

 cup itself, into the now flattened 

 cup-cavity. The adhesive power 

 is apparently in no way dependent 

 upon atmospheric pressure. 



This sexual modification of the 

 front tarsi affords a ready means 

 FIG. i9.-TausoffrontiegofZ^/fcj, o f distinguishing the male from 



showing the large and small suckers. ., f . r ., ,. rc 



the female. A further differen- 

 tiating character is usually, though not always, present upon the 

 elytra. Those of the male are smooth and polished, and but 

 faintly marked by those longitudinal rows of minute punctures ; 

 whereas the elytra of the female are deeply furrowed by a 

 number of longitudinal grooves. But males with furrowed, and 

 females with smooth, elytra are sometimes found. 



The mature animals spend the greater part of their lives in 

 the water, and take flight merely for the purpose of flying to 

 some other piece of water, occasionally plunging into even such 

 small quantities as are contained in a drinking trough or stable 

 bucket. 



Respiration. Inasmuch as Dyticus is unable to extract the 

 oxygen dissolved in the water, periodic visits to the surface for 

 purposes of respiration are necessary. On these occasions the 

 animal floats, tail uppermost, to the surface, and exposes the 

 tip of the abdomen to the air. At the same time the abdomen 

 is separated from the elytra at the apex so as to open a broad 

 cleft leading into the space enclosed between the tightly fitting 

 elytra and the body. A fresh supply of air is thus taken into 

 this chamb p ~ in exchange for the vitiated air which escapes. The 

 elytra and abdomen are then brought again into close contact, 



