[ 73 ] 



IV. 



THE PEESENCE OF LATERAL SPIEACLES IN THE LAEVA OF 



HYPODEEMA. 



By PEOFESSOE GEOEGE H. CAEPENTEE, M.Sc. 



AND 



F. J. S. POLLAED, 

 Eoyal College of Science, Dublin. 



[Plates VIII-XIIL] 



Read February 11. Published Apkil 29, 1918. 



It is well known that in the grubs of most beetles (Coleoptera) and in the 

 caterpillars of moths and butterflies (Lepidoptera) there are paired functional 

 spiracles on one or more of the thoracic segments and on the abdominal 

 segments from the first to the eighth inclusive. But among many of the 

 two-winged flies (Diptera) these breathing-holes are restricted to a large 

 pair at the hinder end of the abdomen, a minute anterior pair, apparently 

 belonging to the prothorax, being sometimes also present : these are the 

 arrangements distinguished by Schiner ('62, p. iv) and Brauer ('69) as " meta- 

 pneustic " and " amphipneustic " respectively, in contrast with the " peri- 

 pneustic " type in which nine or more pairs of spiracles ai*e present, extending 

 in lateral series along the body. Probably no student of the morphology of 

 insect larvae doubts that the metapneustic or amphipneustic condition of the 

 respiratory system has been derived from the more primitive peripneustic 

 condition by the suppression of the intermediate spiracles. This specializa- 

 tion through reduction is correlated with the mode of life followed by many 

 dipteran larvae, the grubs of gnats (Culicidae) and the "rat-tailed maggot" 

 of the drone-flies (Eristalis) living in water and thrusting the tail-end of the 

 body, where the spiracles open, through the surface-film to reach the atmo- 

 sphere above, the maggots of muscoid flies feeding half buried in refuse, 

 decaying organic matter, plant-tissues, or (in the ease of parasites) in animal 

 bodies, where series of lateral spiracles would be useless or dangerous on 

 account of their liability to become choked. This line of speculation is 



R.I. A. PROC, VOL. XXXIV, SECT. B. [7\J 



