LAEV^ OF WATEE-PLIES. 265 



head when it has been skinned. Fig. 162 gives some idea of 

 this curious larva to those who do not know it. At the 

 extremity of the head there are two antenna-like members 

 (a), each of which is terminated with four spines, or claws. 

 The animal is supposed to use these claws in turning over the 

 mud in search of food ; but though I have kept a great many 

 of these larvae for a long time, and watched them closely, I 

 have never seen them so hunt. Perhaps it is because they 

 have always been provided with plenty of the insects upon 

 which they feed. Next to the antennse there is a cluster of 

 ten needle-like bristles, or lancets (6), and just behind these 

 bristles there are two little members somewhat like semi- 

 circular saws. Posterior to these " saws " is a curious upper 

 hp, or labrum, furnished with a kind of brush-like arrange- 

 ment (c). The eye (d) is large and black. In the upper 



J 

 Fig. 162. Larva of Corethra pldmicornis (much enlarged). 



part of the deepest portion of the body there are two au-- 

 sacs (e). Some authorities consider that these air-sacs are 

 very closely connected with the respiratory organs, but others 

 look upon them just simply as " floats." The oesophagus, or 

 gullet (/), leads into a curious and powerful gizzard (n), the 

 use of which can be readily understood when one remembers 

 that this larva, as a rule, feeds upon the smaller fresh-water 

 Crustacea. The gizzard is joined to the stomach (g) by a very 

 narrow channel. The stomach may be seen by the naked 

 eye through the very transparent sides of the creature, and 

 its contents can be pretty plainly observed with the help of 

 the microscope. The stomach is joined to the colon (i) by 

 four very slender tubes or ducts. Between the stomach and 

 the colon there are two posterior air- sacs (/i), which evidently 

 perform the same functions as the anterior ones. There is a 



