some Dij)ferous Larvce. • 603 



(1915, pp. 173-177*), and which are present in all Cyclo- 

 rhaphous larvae ; and (cZ) labial imlps in the form of small 

 conical protrusions, each of which bears a single circular 

 papilla. The ventral surface of the head-lobes is raised in 

 several rows of rib-like projections, armed with strongly 

 chitinised, bifid, reflexed hooks. Each of the three thoracic 

 seynients bears on its anterior part several sinuous rows of 

 small booklets and a definite number of sensory hairs and 

 pits. The vestigial remains of the thoracic legs are repre- 

 sented by six groups, each consisting of three small sensory 

 hairs. The prothoracic segment bears the pair of well- 

 developed anterior spiracles. The first seven ahdununal 

 segments are twice as long as broad ; they present a doubled 

 appearance, owing to the conspicuous zone of articulation, 

 where the segments are telescoped into each other. Each 

 segment bears at its anterior border several sinuous rows 

 of small reflexed booklets. On the ventral surface of the 

 eighth and last abdominal segment is the anus, which divides 

 the segment into an anterior portion resembling that of the 

 preceding abdominal segments and a posterior portion 

 which is prolonged into the respiratory siphon. The 

 })roximal portion of the siphon resembles the corresponding 

 })ortion of an ordinary abdominal segment ; it becomes 

 narrower posteriorly, forming an iLtermediate })ortion which 

 is covered with small, forwardly-directed booklets. The 

 terminal portion of the siphon is slender, rigid, and tubular, 

 and bears the pair of postabdominal spiracles at its 

 extremity. 



The respiratory system of this larva is amphipneustic ; 

 two pairs only of functional spiracles are present — the pro- 

 thoracic and the postabdominal pairs. The prothoracic 

 spiracles (fig. 3, s) comprise eight elongated papilke which, 

 by means of a well-developed felt-chamber, communicate 

 with the two lateral tracheal trunks. The postahdoniiaal 

 sj)iracles (fig. 4) are situated at the extremity of the respi- 

 latory siphon, and, on account of the tip of the latter being 

 bifurcated, are separated from one another by a fairly deep 

 jiroove. Each spiracle appears to possess three spiraculai- 

 clefts, surrounded by long divergent hairs. The felt- 

 chamijer, through which the spiracles communicate with the 

 tiacheal'trunks, is very long and narrow. 



The hucco-pharyngeal organ (fig, 3) shows the structure 

 typical of all the Cyclorhaphous Diptera ; it is comprised of 



* Keilin, D. (1915). " Recherches sur les larves de Dipteres Cyclo- 

 rhaplies," Bidl. Scient. de la France et Belgique, 7* serie, vol. xlix. 

 pu. 15-192. 



o9* 



