88 MR. F. BALFOUR- BROWNE ON THE LIFE-HISTORY 



the variations in colour-pattern within a species*. I have only 

 paid slight attention to the subject, and only in the case of water- 

 beetles, la many of the Hydradephaga one finds a dark ground- 

 colour marked with yellow lines or spots, and there is usually 

 considerable variation to be found within a species, some indi- 

 viduals showing more yellow and others being almost without 

 it. Such species fis Agahus ahh'eviatus Y.,A. didymus 01., and 

 Flatambus macidatus L. are most interesting studies, vihile in 

 such a genus as Deronecies four out of the five Britannic species 

 give excellent material for research. 



To return to Pelohius, In the newly-hatched larva the head is 

 moi'e or less triangular in shape and the prothorax is but little 

 nari'ower than the head, the body thereafter tapering away to 

 the last abdominal segment, which is only about one-fifth the 

 width of the headi 



The larva is heavier than water and breathes subaquatically 

 by means of a series of filamentous gills attached at the sides of 

 the sterna of the thoracic and first three abdominal segments. 

 At the inside of the base of each of the front legs is a tuft of 

 three gill-filaments. Four rather larger filaments lie inside the 

 bases of the middle legs, and the two posterior legs have each a 

 tuft of three gills situated as in the case of the anterior legs. 

 The abdominal gills consist each of a pair of filaments arising 

 from a common base, and one of these is attached on each side to 

 the posterior edge of the stei-nite, those of the first abdominal 

 segment Ij^ing posterior to the pair of embryonic appendages 

 already referred to. 



The gills are tracheate, Avith a single unbranched tube running 

 the length of each filament. 



The legs are long and delicate. The coxa is large, the 

 trochanter consists of two small segments, and the femur, tibia, 

 and tarsvis are each of one segment, the tarsus bearing a pair of 

 claws almost as long as the segment. The tarsus in each case, 

 but more especially of the second and third pairs of legs, is 

 strongly feathered, and therefore forms an eflicient swimming- 

 organ ; but it has also another function. Gilled insect nymphs 

 and larvae, resting in stagnant water, usually adopt some means 

 of circulating the water about the respii-atory apparatus. 

 Agrionid dragonfly nymphs Avill frequently lash the abdomen 

 from side to side ; the nymphs of the Ephemerid, Chloeov. flap 

 the lamellate gills ranged along the sides of the abdomen, and the 

 larvfe of certain Perlids " dance " up and down, lajsing and 

 lowering the body betAveen the legs. The larvae of Pelobms use 

 their feathered legs as fans, the middle leg on one side and the 

 anterior and posterior legs on the other being raised off the 



* Vide Brown, Aiinetta ¥., "Evolution of Colour-pattern in LifJiocoUetis." 

 Journ. Acad. Nat. Sci. Philadelphia, xvi. (1914) pp. 105-165; and Palmer, Miriam A., 

 " Some Notes on Heredity in the Coccinellid genus Adalia Mulsant." Ann. Ent. 

 Soc. America, iv. (1911) pp. 283-308. 



