758 Mr. Frank Balfour Browne [May 9, 



contracting and expanding the body it exhales the used-up air and 

 inhales fresh air. 



For a day or so after hatching the larva is soft and is not hungry, 

 but once its skin and jaws have hardened it begins to look about for 

 food. I found that tadpoles and pieces of chopped worm were 

 suitable food, but under natural conditions small newts, water-shrimps 

 and insect larvse — including brothers and sisters— constitute the 

 normal diet. It is impossible to keep two larvae together in one 

 small vessel, as one invariably attacks and kills the other within a 

 few hours. Even when I gave a tub to four specimens only one 

 survived after a few weeks, so that in a small loch, where at least some 

 thousands of these larvae hatch out, the death-rate must be enormous. 



The method of feeding of the larva is peculiar. The two long 

 sharply-pointed jaws are each pierced with a fine tube, one end of 

 which opens on the inner side just below the apex, and the other 

 end of which opens on the upper side just near the base. When the 

 jaws are closed the inner ends of these tubes communicate with the 

 corners of the mouth, but when the jaws are open the inner ends of 

 these tubes do not communicate with the mouth at all. The mouth 

 itself is also peculiar. In a front view of the head it is visible as a 

 long narrow slit between the bases of the jaws, but if this slit is 

 examined it is found that across the lower side of it is a raised ridge 

 which fits into a groove running across the upper side of it. When 

 the jaws are wide apart the ridge and groove are separated, and the 

 mouth is open, but as soon as the jaws come together the ridge fits 

 into the groove, and the mouth is closed. As soon, therefore, as the 

 larva seizes its prey its mouth is closed, and the only communication 

 into it is through the tubes in the jaws, the basal ends of which now 

 open into the corners of the mouth. 



Immediately behind the mouth is the powerful sucking-pump, the 

 pharynx, which I mentioned in connexion with the embryo. By 

 expansion and contraction of its muscles it sucks in the juices of the 

 prey through the tubes in the jaws. But if this were the whole pro- 

 cess of feeding there would be a considerable waste, as a worm or a 

 tadpole consists of a large amount of solid material ; and yet, if one 

 watches one of these larvge feeding, one will find that almost nothing 

 is left of the prey except the skin. This is due to the fact that at 

 short intervals the sucking-pump stops working and saliva is poured 

 into the prey. This saliva digests and dissolves away the solid parts 

 of the food, which are then sucked in by the larva. The process of 

 digestion, which in most animals takes place internally, is carried 

 on in tliese larva outside the body. 



With regard to the duration of the larval period, in my examples 

 this varied from six to nine weeks. This period is divided into three 

 stages, there being two moults prior to the final one which produces 

 the pupa. Each of the first two stages only lasts about ten days, so 

 that the last stage is a very long one, as it is in all other insects! 



