590 Will. 8. Marshall, 



where the wing veins are present, come together soon after the wing 

 becomes external, then follows the peciiliar elongation of the hypo- 

 dermal cells already noticed in the developing wings of many insects. 



Xot only are tracheae absent from the developing wings before 

 their expulsion from the peripodial cavity in Platyphylax but at no 

 time do we find the close association with the rudiment of any extra 

 development of tracheae which has been seen in other insects. In 

 the earlier stages there was found a slight development of tracheae at 

 the base of the rudiment (Figs. 8, 12 and 13, Tr) but not so marked 

 as that seen by other observers in the insects they studied. Tracheae 

 were first seen within the developing wings sometime after they had 

 become external but were then noticeable only in sections. After 

 the wings finally become straightened in the young pupae each one 

 can be seen to receive a brauch from the longitudinal trunk of the 

 side on which it is situated. 



After the wing becomes external the markings are seen to be more 

 regulär than they were on the internal rudiment and there is a simi- 

 larity in appearance in either meso- or metathoracic rudiments in 

 larvae of about the same stage of development. We earlier noted the 

 fact that soon after their first appearance the markings became separable 

 into two groups each group lying near the more anterior or the more 

 posterior margin of the rudiment (Figs. 15 and 16 and Text figure VI). 

 As the rudiment becomes beut and crowded within the peripodial 

 cavity these different markings become harder to distinguish and 

 to accurately follow from stage to stage. Each wing rudiment, 

 foUowing its expulsion from the interior, straightens and the markings 

 become regulär and clearly defined. Tlie two groups of markings are 

 easily distinguished and also a third which was earlier represented by 

 a few dark lines at the more dorsal margin of the wing rudiment. These 

 three groups would now become the proximal, median and distal group, 

 the two last of these correspond to the only two groups present in the 

 earliest stages. The wings after becoming external continue to enlarge 

 and for some time the wing veins can be easily traced. As long as 

 the last larval skin remains intact the wings occupy a clearly defined 

 and restricted space and their continued growth results in a second 

 period in which they become bent and folded. This folding is generally 

 first noticed by indentations along the anterior margin of the wing, 

 these are then followed by one or more horizontal folds (Figs. 22 and 23). 

 Figure 22 shows the wings of a young pupa just after the last larval 

 skin has split but before it has been removed from around the body 



