&2 MR. F. BALFOUR-BROWNE ON THE LIFE-UISTORY 



The mechanism of all this complex apparatus seems to be as 

 follows : — The Pelohius larva pounces upon tlie Titbifex and, by 

 expanding the oesophagus, sucks the end of the worm into the 

 stomodfeum, and the mandibles then close so that the prey is held 

 either between the two, or more usually, between the upper and 

 the epipharynx. I think, therefore, that it usually passes into 

 the mouth between the two lobes of the epipharynx {v. PI. I. 

 figs. 11 & 12). 



At the moment of seizing upon the worm the maxillfe and 

 labium are shot forward and the prey is received into the "scoop,' 

 and these parts then retract, the flap in the "scoop"' pressing 

 the worm upwards into the epipharyngeal slit, and the closing 

 of the jaws bending the body of the worm upwards so that it 

 is completely jammed and cannot move backwards or forwards 

 {v. PL I. fig. 12). At the first suck, the end of the worm pre- 

 sumably reaches well down into the pro-ventricular mill, where 

 it is well bruised, and, when this portion has been sufficiently 

 crushed, the hold upon the worm is momentarily relaxed by the 

 opening of the jaws and the shooting forward of the maxillfe and 

 labium ; the sucking action is repeated, and once again the mouth- 

 parts jam the body until another section has been crushed by 

 the pro-ventricular mill. 



4 (g) Habits of the fidl-groimi Larva. 



The larva is full-fed about twenty-two days after the second 

 moult, by which time it measures about 15 mm. in length, the 

 median " tail " adding another 5 mm., and it is now ready to 

 leave the water. In my tumblers it was always evident when 

 this stage was reached, because the larva would swim round and 

 round at the surface and endeavour to climb up the glass. 



As I wished to watch the work of the larva in forming its 

 pupal cell in the earth, I tried, with this species, the same 

 method as I had used successfully with Dytisctis lajjponicus — that 

 is, I placed the larvse in an earth-bottomed vivarium with a glass 

 side, made an artificial burrow in the ea,rth against the glass, and 

 carefully directed the steps of the larva, to the entrance of the 

 burrow, closing the mouth of the latter when the larva had 

 entered. With this species, however, the method did not work 

 so successfully, as the larva, having reached the end of the 

 artificial burrow, usually continued it on its own account and as 

 a rule in a direction away from the glass. Digging up such larvfe 

 and starting them again seemed to discourage them, and they 

 were a.pt to sulk and make no cell at all. 



I therefore devised a special glass cell consisting of two lantern- 

 slide cover-glasses. Between these two, at adjacent corners, two 

 small pieces of cork, half an inch thick, were placed so that, along 

 one side, these two plates could not come into contact. Along the 

 opposite side the two plates were brought into contact and held 



