836 bulletin: museum of comparative zoology.- 



group of muscles, with the exception of three larval muscles which 

 degenerate during pupal life. Two of these muscles (Plate 1, Figure 3, 

 A, fj.) extend dorso-ventrally along the suture hetween the meso- and 

 metathorax. They do not disappear for some time, and are shown in 

 the figure of the pupa (Plate 3, Figure 7, X ; Plate 2, Figure 5, /a). The 

 third of these degenerating muscles (Plate 1, Figures 3, 4, v) extends the 

 full length of the metathorax. It lies in the lateral part of the somite 

 extending obliquely from antero-dorsal to postero-ventral. This muscle 

 is one of the first to disappear, and so is not shown in the figure of the 

 pupa. 



(3) TJie ventral anfero-posterior group consists in the larva of eight 

 muscles, five of which fuse to form the single representative of this group 

 in the imago. This muscle is shown in the reconstruction drawings 

 only in the pupa (Plate 3, Figure 7, rfr. ms'thx. if.) and in the imago 

 (Plate 5, Figure 11, rtr.ms'thx.if.); in both the view is from the left 

 side of the insect. Cross sections of this group {rtr. ms'thx. if., 0, i, k) 

 are shown in Figure 10 (Plate 4) for the larva, and in Figure 12 

 (Plate 5) for the young pupa. 



Retractor mesothoracis inferior of Luks. 

 (Pretradeur de Vapophyse episternali posterieure of Straus-Dilrckheim.) 



The five larval muscles (Plate 4, Figure 10, rtr. ms'thx. if), all of 

 which extend the full length of the somite, become in the pupa (Plate 5, 

 Figure 7, rtr. ms'thx. if.) closely approximated to form a single muscle. 

 This, by the ingrowth of the meso- and metafurcae, comes to have in the 

 imago the position shown in Figure 11, rtr. ms'thx. if (Plate 5). Here 

 its origin is seen to be on the anterior lateral horn of the metafurca 

 (inffur. 1) and its insertion on the mesofurca (msfur.). 



The three remaining larval muscles of this group (0, i, k), degenerate 

 during pupal life (Figure 10, larva; Figure 12, pupa). These muscles 

 extend the full length of the somite, form the deeper layer of this group, 

 and present in general the same characteristics as the degenerating 

 muscles of the dorsal group. 



Summing up the changes which take place in the muscles of the meta- 

 thorax during pupal life, we find : 



a. That not a single larval muscle persists unaltered from larva to 

 imago. 



h. That the great majority of the larval muscles metamorphose into 

 adult muscles, and 



