TKANSFOllMATIONS OF THE INSECT. T.') 



In the metamorphosis of Corethra, a Mosquito-hke Fly, which 

 is active both in the larva and pnpa states, '"the segments of 

 the larva are converted directly into the corresponding seg- 

 ments of the body of the imago, the appendages of the head 

 into the corresponding ones of the head of the imago ; those 

 of the thorax are produced after the last moult of the larva 

 as diverticula of the hypodermis round a nerve or trachea, 

 from the cellular envelope of which the formation of tissue in 

 the interior of the appendages issues. The larval muscles of 

 the abdominal segments are transferred michanged into the 

 imago ; the thoracic muscles peculiar to the imago, as also 

 some additional abdominal muscles, are developed in the last 

 larval periods from indifferent cellular cords which are indi- 

 cated even in the egg. The genital glands date back to the 

 embryo, and are gTadually developed ; all tlie other systems of 

 organs pass with little or no alteration into the imago. P^atty 

 body aione or inconsiderable. Pupa-state short and active." 

 (Weismann.) 



As the two tj'pes are most clearly discriminated by the 

 l)resence or absence of true imaginal disks, AYeismann suggests 

 that those insects which undergo a marked metamorphosis 

 might be divided into Insecta discota (or Insects with imaginal 

 disks), and those without, into Insecta adiscota. 



The metamorphosis of Corethra may prove to be a type of 

 that of all insects which are active in their preparatory stages ; 

 and that of Mitsca typical of all those that are quiescent in the 

 pupa-state, at least the Lepidoptera and those Dipteia which 

 have a coarctate * pupa, together with the Coleoptera and those 

 Neuroptera in which the metamorphosis is complete, as Phrij- 

 ifa)iea, Ilemerohius^ etc. 



The transformations of the Ilumble-bee are easilj' observed 

 by taking a nest after the first brood have matured, when we 

 shall find individuals in all stages of development from the 

 larva to the imago state. The figures below show four stages, 

 but in reality there is every gradation between these stages. 



'The larva? of somo of the higher Diptcra spin .1 slight cocoon, while the tnio 

 flics, such as the Muscida,' and Syrphida;, etc., change to pupa' within the larva 

 skin which contracts into a cylindrical "pnparium" coiTcsponding in use to the 

 i'ocoon; such pujia? arc called "coariitatc."' 



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