VII 



LARVA PUPA 



451 



enor 



stigma of the larva of Lip- 

 am lucens. , One of the 

 three " Knospen " or lobes ; 

 b, external stigmatic scar ; 

 <.', internal scar ; d, stig- 

 matic chamber (Filzkam- 

 mer) ; e, trachea. (After 

 Meijere.) 



considered the original tracheal tube, opening externally as an 



external stigmatic scar " Stigmennarbe " and with a second 



or inner scar placed internally. We may 



conclude from what is already known 



that these structures will be found to 



differ in the same larva according to the 



stage of its development. 



An extremely valuable summary of 

 the characters and variety of Dipterous 

 larvae has been given by Brauer, 1 from 

 which it appears that the larvae of the 

 first half of the family exhibit great 

 variety and have been much studied, FlG- 218. The post 

 while the more purely maggot-like forms 

 of the Muscidae have, with one or two 

 exceptions, been little investigated. 



The pupal instar is of two distinct 

 kinds. First, we meet with a pupa like that 

 of Lepidoptera, viz. a mummy-like object, 

 or pupa obtecta, in which there is a crisp outer shell, formed 

 in part by the adherent cases of the appendages of the future 

 imago. This condition, with a few exceptions to be subsequently 

 noticed, obtains in the Nemocera and Brachycera. It is exhibited 

 in various degrees of perfection, being most complete in Tipulidae ; 

 in other forms the shell is softer and the appendages more pro- 

 tuberant. The second kind of pupa is found in the Cyclor- 

 rhaphous flies ; it has externally no marks except some faint 

 circular rings and, frequently, a pair of projections from near 

 one extremity of the body ; occasionally there is a single pro- 

 minence at the other extremity of the body. This condition is 

 due to the fact that the larva does not escape from the skin 

 at the last ecdysis, but merely shrinks within it, so that the 

 larval skin, itself contracted and altered by an excretion of 

 chitin, remains and forms a perfect protection to the included 

 organism. This kind of pupa looks like a seed, and is well 

 exemplified by the common Blow-fly. The capacity for entering 

 on such a condition is evidently correlative with the absence of a 

 larval head. The metamorphosis in this curious little barrel 

 goes on in a different manner to what it does in the pupa 



1 Denk. Ak. Wicn, xlvii. 1883, pp. 1-100, pis. i.-v. 



