362 INSECT A. 



(a few burrowing caterpillars). Usually, three pairs of short, jointed thoracic 

 limbs and five pairs of abdominal limbs are present. The latter are found on 

 the third to the sixth abdominal segment, and on the terminal segment as the 

 so-called prologs. They are truncated, and have a bilobate or circular sole 

 beset with minute hooks. In Ncpticula, there are in all eighteen limbs. In 

 other cases, the number is diminished by the reduction of the abdominal pairs, 

 in some caterpillars, only two or three abdominal pairs of limbs being found 

 (on the sixth to the ninth abdominal segment) besides the three thoracic pairs. 



The pupa is a mummy pupa (pupa obtccta), and is frequently enclosed in a 

 cocoon. In a few Tincidae (especially in Microptcryx), the limbs are said to 

 be partly free. The mouth-parts in their structure essentially resemble those 

 of the imago. 



Diptera. The larvae of the Diptera must in general be regarded as essentially 

 degenerate forms. The variation found in the different sub-groups is all the 

 greater on this account. "We have here the best examples of the type of limbless, 

 soft-skinned "maggots," whose body consists of a number of similar rings. 

 Functional thoracic limbs are always wanting, and vestiges are only found on 

 the first thoracic segment. In the same way, truncated ventral feet occasionally 

 develop on the abdominal segments. The mouth-parts also are often quite 

 vestigial. In most cases the integument is soft, but it may be of a firmer 

 character (Slratiomys, in the larval skin of which, according -to Leydig, lime 

 salts are deposited). The soft constitution of the integument may also extend 

 to the cephalic segments (headless larvae) ; at this part, as a rule, however, a 

 chitinous oesophageal framework develops, or a more or less marked maxillary 

 capsule. But only in those cases in which this chitinous capsule contains the 

 cephalic ganglia is it designated as the actual " head " (Brauer, encephalic larvae). 



The pupa is not always quiescent. In individual cases (Culicidae) it moves 

 about in the water by the contraction of the abdomen. The resting pupa 

 is often enveloped in the larval integument, and is then known as the barrel- 

 shaped pupa. It is either free-limbed (x>upa libera), or, like the Lepidopteran 

 pupae, is provided with limbs glued to the body (pupa obtccta, mummy pupa). 



The forms assumed by the Diptera larvae are utilised by Brauer (No. 100) 

 for systematic purposes. He distinguishes two principal types, according to 

 the manner in which the larval integument splits before the pupal stage is 

 entered upon (or, in cases in which a barrel-like pupa is formed, when the 

 imago hatches): (1) the Orthorhapha, in which, as a rule, a longitudinal slit 

 opens on the back and a transverse slit at right angles to it ; (2) Cyclorliapha, 

 in which the slit is a circular one, transverse to the long axis of the pupa, so 

 that one or two caps are pushed off at the anterior pole. To the first type 

 belong the encephalic larvae of the Culicidae and Chironomidac, and further 

 the larvae of the Tipulidac, Cecidomyiidac, Stratiomyidae, etc., while the 

 Muscidac, Syrphidae, and Pupipara belong to the second type. 



Great variety prevails with regard to the condition of the respiratory organs. 

 Many larvae breathe only through the last pair of stigmata at the posterior end 

 of the body which have remained open (mctapneustic respiration), in others a 

 pair of anterior pro-thoracic stigmata remain open in addition to the posterior 

 pair, while the others are closed (umphipncustic respiration); again, in other 

 cases, some of the intermediate stigmata are also partly open (pcripneustic 

 respiration). The pupae of many forms, on the other hand, breathe only through 

 the most anterior pair of stigmata which occur on the pro-thorax (propncustic 

 respiration). 



