670 TEXT-BOOK OF ENTOMOLOGY 



hypertrophy of the neurilemma of a nerve passing down from within into 

 the imaginal bud, and held that nerves and tracheal branches soon after passed 

 into the inner surface of the imaginal bud. (Korschelt and Heider. ) 



When the imaginal buds of the appendages enlarge, then the 

 peripodal membranes become correspondingly distended, and the 

 limbs within assume a more or less crumpled position, and in Core- 

 thra are spirally twisted, while the rudiments of the wings are 

 folded. The completion of the rudimentary limbs is accomplished 

 simply by their passing out of the invagination in which they origi- 

 nated. The limbs thus gradually become free, the peripodal mem- 

 brane is seen to reach the level of the rest of the hypodermis and 

 become a part of it, and the base of the extremity is no longer 

 situated in a cavity. 



The internal organs of Corethra undergo but to a slight degree 

 the destruction (histolysis) which is so thoroughgoing in the Muscidae. 

 Kowalevsky states that in the mid-intestine of Corethra a histolysis 

 of the larval and reconstruction of the imaginal epithelium goes on 

 in the same way as has been described in Musca. Most of the 

 larval organs pass without histolytic changes directly over into those 

 of the pupal and imaginal stages ; the muscles in general are also 

 unchanged, but those of the appendages and wings are made over 

 anew. The last arise, according to Weismann, in the last larval 

 stage from strings of cells which are already present in the 

 embryo. 



When we consider how insignificant the internal transformations 

 are during the metamorphosis of the Tipulidae, of which Corethra 

 serves as an example, we can scarcely doubt that we here have 

 before us conditions which illustrate the passage between an incom- 

 plete and a complete metamorphosis. Thus, among other things, 

 should be mentioned the short duration of the pupa stage and the 

 activity of the pupa, as also the early appearance of the germs of 

 the compound eyes, a character which Corethra has in common 

 with the Hemimetabola. (Korschelt and Heider.) 



Formation of the imago in Culex. In respect to the formation of 

 the imaginal head, Culex is still more primitive than Corethra. 

 Miall and Hammond find from Hurst's partly unpublished descrip- 

 tions and preparations that there are no deep invaginations for the 

 compound eyes or antennae of the imago. 



" The compound eye forms beneath the larval eye-spots, and is at first rela- 

 tively simple and composed of few facets. The number increases by the gradual 

 formation of partial and marginal invaginations, each of which forms a new 

 element. The imaginal antenna grows to a much greater length than that of 



