94 TAirrnI atnl Pupal Stages of Bibio Johannis L. 



but they are not so well developed as in the full-grown larva, the setae 

 being shorter and fewer in number. 



In the labium, the submentum is rather less stout than that of the 

 full-grown larva, the anterior projections are longer and sharper, while 

 between them is a third projection. 



Alimentary Canal. The alimentary canal of the young larva is 

 similar to that of the adult larva. The caeca are rather wider in pro- 

 portion to their length, and are filled with a yellow fluid. The peri- 

 trophic membrane is present as a straight delicate tube lying inside the 

 mesenteron, and extending from its anterior end to about the point at 

 which the posterior caecum opens into the digestive system. The 

 Malpighian tubes are similar to those of the fully grown larva, entering 

 the alimentary canal by a common duct, but the tubes are not enlarged 

 at their point of union. They are colourless, but contain numerous light 

 yellow granules. 



Tracheal System. From each spiracle of the pair on the last segment 

 a single short trunk passes inwards, dividing into two on entering the 

 body. One of these branches passes forwards laterally, giving off a fine 

 transverse branch in each segment which connects with the main lateral 

 trunk of the other side ; in each segment, except the second and eleventh, 

 a short branch is given off which passes outwards to the cuticle, but has 

 no opening to the outside (Text-fig. 12, p. 114). 



From the transverse connective in the first segment, and from the 

 main lateral. trunks, a number of branches enter the head and are dis- 

 tributed there. 



From the lateral trunks in the eleventh and twelfth segments and 

 from the transverse connective in the twelfth segment a number of fine 

 branches are given off which pass to the heart. 



The second of the two branches (into which the trunk from the 

 spiracle divides on entering the body) again divides into a number of 

 finer branches. Most of these branches are distributed in the twelfth 

 segment, but one branch passes forwards, and divides into two at the 

 end of the eleventh segment. The finer of these branches passes to the 

 loop in the alimentary canal, while the other passes forwards into the 

 head outside the main longitudinal trunk. This lateral trunk connects 

 with the branch which passes outwards from the main trunk in each 

 segment, except the second and eleyenth. 



Circulatory System,. The heart lies in segment eleven and in the 

 anterior part of segment twelve; it is continued forward as a dorsal 

 vessel of slightly narrower calibre, to the anterior end of the body. 



