vii ANATOMY LARVAE 449 



is by no means extensive. The tracheal system is highly developed, 

 and has air-sacs connected with it ; a large pair at the base of 

 the abdomen being called aerostats by Dufour. Inside the 

 thoracic spiracles there are peculiar structures supposed by some 

 to be voice-organs, while the abdominal spiracles are said to be 

 remarkably simple in structure. Lowrie says that there are ten 

 or eleven pairs of spiracles in the Blow-fly ; one of these, near 

 the base of the wing, is peculiar in structure, and may not be 

 a true stigma ; he calls it a tympanic spiracle ; it seems doubtful 

 whether there are more than seven abdominal pairs. The alimen- 

 tary canal is very elongate, and is provided with a diverticulum, 

 the crop; this is usually called the sucking stomach, though its func- 

 tion is extremely doubtful. The Malpighian tubes are four in 

 number, and are very elongate ; in several groups of Nemocera 

 there are, however, five Malpighian tubes, a number known to 

 occur in only very few other Insects. The nervous system is 

 remarkable 011 account of the concentration of ganglia in the 

 thorax, so as to form a thoracic, in addition to the usual cephalic, 

 brain. For particulars as to the positions of the ganglia and the 

 great changes that occur in the lifetime, the student should 

 refer to Brandt, to Kiinckel, and to Brauer. 1 Much information 

 as to the internal anatomy of the Blowfly is given by Lowne, but 

 it is doubtful to what extent it is applicable to Diptera in 

 general. 2 



The larvae of Diptera are so far as the unaided eye is 

 concerned without exception destitute of any kind of adorn- 

 ment, the vast majority of them being of the kind known as 

 maggots. None of them have 

 true thoracic legs; though in 

 the earlier groups, pseudopods 

 or protuberances of the body 



that Serve as aids in loCOmo- Fio. 217. Acephalous larva or maggot of the 

 tion are Common. Unlike Wow-fly, with the head, , extended. (After 



Lowne. ) 



what occurs in other Orders 



the arrangement of these pseudopods on the body differs greatly 



in various forms; in a few cases they are surmounted by 



1 Brandt, Horae Soc. ent. Ross. xiv. 1878, p. vii. ; xv. 1879, p. 20. Brauer, 

 Denk. Ak. Wien, xlvii. 1883, pp. 12-16. Kiinckel, C.E. Ac. Paris, Ixxxrx. 1879, 

 p. 491. 



2 Blow-fly, 1895 : in two vols. For Anatomy of Volucclla, see Kiinckel 

 d'Herculais, Recherches sur Vorg. des Volucelles, Paris, 1875 and 1881. 



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