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XXXIII. Notice on the harvcc of Diptera. By William 

 Sharp MacLeay, E&q,^ F.L.S. 



To Richard Taylor^ Esq. 



"VrO order of insects affords greater proof of the necessity 

 •^ of generalizing, than that of Diptera. We often hear of 

 the last joint of the antennje in this order terminating in a 

 bristle, or being furnished with a lateral one ; whereas this 

 bristle is essentially part of the antennee, being in fact articu- 

 lated, and composed of as many joints as with the thicker ones 

 will make up the proper number that characterizes the family. 

 The true description therefore of the antennas in Musca vomi- 

 foria is, that the last three joints compose a seta or bristle in- 

 serted laterally at the extremity of the third joint. 



Owing moreover to the rarity of generalization in this science, 

 I find on looking over the various entomological works that 

 have been hitherto published, that whenever the larvee of 

 Diptera fall under consideration, they are altogether errone- 

 ously described. The head of each species when fully ex- 

 serted is not of a variable but of a constant form, and like that 

 of other insects is provided with two articulated anteimas. 

 These antennae are simple and triarticulate in the larvae of the 

 Muscid<s, and under a high power are to be seen situated on 

 that bimammillary frons which was known to Reaumur, but 

 owing probably to the minuteness of the object has been al- 

 ways badly figured, and was not at all understood by him. (See 

 Memoires pour Hist, dcs Ins. vol. iv. pi. 34. fig. 3, dd.) De- 

 geer has represented them as minute tubercles (vol. vi. pi. 3. 

 fig. 12) ; but either from not accurately investigating them or 

 from not using a high power, and above all from not genera- 

 lizing, he also remained ignorant of their articulated structure 

 and of their being true antennae. This is the more extraor- 

 dinary, as the antennae of those larvee of Diptera, such as the 

 Culicidcc, &c. which have not a retractile head have been long 

 known and figured, and in some cases (as Degeer, vol. vi. 

 pi. 18. p. 8), are so like the antennae in the larvjH of Mnscidce, 

 that it surprises one not a little that these last should have 

 been so long imagined to be destitute of antennas. 



What have been by some entomologists termed the singu- 

 lar anterior prolegs of Tanypiis inaculafiis, will be found on 

 accurate examination to be the two anterior pedunculated 

 spiracula, which, from the insect being aquatic, necessarily take 

 a branchial form. The posterior ^^ prologs " are also pedun- 

 culated branchial spiracuhi of the same kind. All those or- 

 gans, whether retractile or not, which are called anterior 

 prolegs, and tentacula in Chironomus, Tatiypus^ &c. are the an- 

 terior 



