THE INTERNAL STRUCTURE OP THE LEPIDOPTEROUS PUPA. 85 



their full development, and those numerous and most intricate plexus 

 of nerves in the three thoracic segments of the larva form only a few 

 trunks, which can hardly be recognised as the same structures. The 

 whole of these important changes are thus seen to take place within 

 the first three days after the insect has undergone its metamorphosis, 

 and they precede those of the alimentary canal, generative system, and 

 other organs, which are still very far from being* completed, and, indeed, 

 as compared with the nervous system, have made but little progress 

 (Art. Insecta, pp. 962-965). 



It may be noted that no such extensive changes as are here 

 described occur in some Lepidoptera. In the grublike apterous female 

 of the higher Psychids very little change in the nervous system takes 

 place and the ganglia, still separate in most of the segments, are readily 

 examined owing to their dark colour showing through the almost trans- 

 parent skin. 



The development of the genital organs has been studied by many 

 anatomists and Jackson states (Trans. Linn. Soc. Lond., 2nd ser., 

 v., p. 174) that there are three stages traceable in the evolution of the 

 genital ducts in the Lepidoptera, viz., (1) An Ephemeridal stage, 

 which ends towards the close of larval life. (2) An Orthopteran 

 stage, indicated during the quiescent period preceding pupation. (3) 

 A Lepidopteran stage, which begins with the commencement of pupal life. 

 This raises many interesting suggestions respecting the development of 

 these organs in the pupal stage, by means of which they reach, before 

 the emergence of the imago, their final development. Jackson writes : 

 " In the full-grown female larva of Pieris brassicae, the species investi- 

 gated by Herold, the larval oviducts which are continuous with the 

 larval ovaries run backwards near the dorsal middle line, pass 

 betAveen the trachea? given off from the 7th pair of stigmata and are 

 attached to the main trachea of the bundle by a filament ; they each 

 turn towards the ventral middle line in the 7th somite, behind the 7th 

 stigmata, pass beneath the main longitudinal and oblique muscles of 

 the somite, and are attached close together to the hypodermis in the 

 middle ventral line at the posterior margin of the 7th somite. From 

 the attached ends of the larval oviducts start fine longitudinal striae, 

 which traverse the 8th sternal region and connect the larval oviduct 

 to a white mass composed of two oval pieces attached to the hypo- 

 dermis beneath the rectum upon the intersegmental membrane imme- 

 diately following the 8th somite. During the quiescent stage pre- 

 ceding pupation, the two oval pieces become approximated to the ends 

 of the larval oviducts, owing to a shortening or contraction of the 

 hypodermis. As soon as pupation has taken place, they fuse with the 

 oviducts and acquire a soft loose consistence. During the pupal state 

 the two larval oviducts fuse together, at their point of union with the 

 oval pieces, to constitute the common (i.e., the azygos) oviduct, whilst 

 the oval pieces give rise to three processes, a left larger, the rudiment 

 of the bursa copulatrix (Herold's ' Samenbehalter '), a right smaller, 

 the rudiment of the receptaculum seminis (Herold's ' ein-horniges 

 Absonderun^sorgan'), and a bifid posterior, the paired sebaceous gland 

 (Herold's ' zwei-horniges Absonderungsorgan '). The mass which 

 gives rise to these processes disappears, whilst they increase in size 

 and acquire the form they possess in the imago." 



Suckow's investigations were carried out on Dendrolimm pini. 



