336 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, 
X, ») extend dorso-ventrally along the suture between the meso- and 
metathorax. They do not disappear for some time, and are shown in 
the figure of the pupa (Plate 3, Figure 7,2; Plate 2, Figure 5, »). 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) The ventral antero-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, rtr. 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 (7tr. ms’tha. if., 0, 1, 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. 
(Prétracteur de Vapophyse épisternali postériewre of Straus-Dirckheim.) 
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 
amago 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 
(mt fur. 1) and its insertion on the mesofurca (ms'fur.). 
The three remaining larval muscles of this group (0, 1, x), 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. 
b. That the great majority of the larval muscles metamorphose into 
adult muscles, and 
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