*pir acute, or breathing holes. These are situ- 

 ated in the true larva, or caterpillar, in the 

 second, fifth, sixth, and following segments to 

 the twelfth. This is the general structure of 

 the larva, but there are modifications of it in 

 every particular. Thus, in the larva of those 

 Hymenopterous insects which are entirely desti- 

 tute of feet, there are fourteen distinct segments 

 in the body, besides an anal tubercle, and ten 

 spiraculae on each side (Jig. 356). These are 



INSECTA. 



noticed fourteen (Jig. 358). 



871 

 The first four of 



Fig. 358. 



Fig. 356. 



Fig. 357. 



Lateral view. Inferior view. 



Larva of Vespa crabro, magnified. 



situated in the second, third, fourth, and remain- 

 ing segments to the twelfth, so that in these in- 

 sects the thoracic portion of the body contains 

 an additional spiracle, while the abdomen has 

 one additional segment. This fact is particularly 

 interesting from the circumstance of its appa- 

 rently disturbing the opinions hitherto advocated 

 by naturalists respecting the normal number of 

 segments, which has been thought to be con- 

 stantly thirteen in this class of invertebrata, while 

 it derives a greater importance from theadditional 

 segment belonging to the abdomen, as we shall 

 hereafter prove. This additional number of 

 segments, as constantly occurring in apodal 

 Hymenoptera, was first pointed out by Mr. 

 Westwood,* and has been observed by ourselves 

 in every instance in the larvae of Vespa Crabro, 

 (fig. 356.) Bombus terrestris, Anthophora 

 retusa, Ichneumon Atropos, and other species. 

 In the common maggots or larvae of the flesh- 

 flies, Muscida, the body is elongated, and 

 tapering at its anterior extremity, and con- 

 sists of fourteen segments.t In the larva of a 

 species of Muse a which infests bacon and other 

 dried provisions, and in that of the common 

 flesh-fly, Musca vomitoria, we have distinctly 



* Trans. Ent. Soc. vol. ii. p. 124. 



t Fifteen, if we include the anterior portion of 

 the third segment, which appears like a distinct 

 part. Since these observations have been in print 

 the XII. and XIII. Parts of Mr. Westwood's " In- 

 troduction " have been published, and it is grati- 

 fying to observe that he has found fifteen segments, 

 including the head, in the larva of Odynerus, Col- 

 letes, and Anthidium. 



A , Apodal larva of Musca ; B, headofdo.: a, mandi- 

 btilar hooks ; b, the anterior bronchia; c, the labnan ; 

 C, organs of respiration ; D, a portion of the dorsalvessel. 



these appear to constitute the head of the larva, 

 since in them are contained the palpi and oral 

 apparatus, besides two remarkable orange- 

 coloured organs, which project from the sides 

 of the fourth segment, and on a cursory view 

 appear to be the organs of vision, but are in 

 reality the branchiae of the future pro-thorax 

 (B A). In the larva of the sheep-hot, CEstrus 

 ovis, which resides for many months in the 

 frontal sinuses and roots of the horns of that 

 animal, there are thirteen segments, but the 

 terminal one is very indistinct, while the an- 

 terior one, which is exceedingly minute, is 

 proved to form a large proportion of the head, 

 by its containing the oral apparatus, and by 

 the existence in it, at its anterior part, of two 

 very distinct eyes. These larvae respire by 

 means of two sets of branchiated organs, 

 (fig. 358, c) situated at the posterior part 

 of the body, and not by lateral spiracles. 

 The apparently anomalous condition of the 

 head in these insects, like the additional 

 segment in Hymenoptera, is a circumstance 

 of much interest, but is not without its 

 parallel in perfect individuals of other classes, 

 as in ' Myriapoda, in which the head is most 

 distinctly composed of at least three seg- 

 ments. We must not conclude, however, with 

 Dr. Ratzeburg, as noticed by Mr. West- 

 wood,* that in Hymenoptera the head of the 

 Imago corresponds to the first two segments 

 of the larva, because at the latter period of 

 the larva state, just before the insect becomes 



* Trans. Ent. Soc. vol. ii. p. 125. 



