OF THE LARVA OF PYGÆRA BUCEPHALA. 181 
Nos. 59 and 60 have united together. 
No. 61 overlaps 60 at the fore end. 
No. 63 is generally, if not always, double. 
First Thoracic Segment.—In the posterior part of this segment several muscles are 
wanting, and in the anterior they differ widely from the usual type, being principally 
modified so as to effect rotations of the head. 1 
The most striking alteration is the presence of the muscle marked 82 (C+of Lyonet), 
which is attached in front to the posterior border of the head, and passing through the 
present segment is attached by four heads along the middle dorsal line of the second 
thoracic segment; nor did it vary in any of the specimens examined by me. There does 
not seem to be any muscle comparable to it in the other segments. There are yet three 
other muscles which seem to be peculiar to this segment. No. 80 rises close to the fore 
end of 82, and passing over 19, 20 and 26, is attached by two heads near the middle 
ventral line, close to 56. No. 81 rises with the preceding and follows nearly the same 
course, but passes under 19, 20 and 26. No. 83 rises from the fore side of the spiracle 
and passes forward to the upper end of 46. 
No. 1 is in this segment divided into two or three separate muscles, which are attached 
side by side behind, and fixed to the fore part of the segment, or rather into the mem- 
brane connecting the head with the thorax. 
No. 4 is attached in front, close to 1. 
No. 5 is double; in some cases however it is united in front. The one fascicle rises 
under or at the side of 1, the other rather further down, and both are inserted on the 
ventral side of 4. 
No. 7 lies at the lower side of 6 and parallel to it. ; 
No. 8 perhaps is wrongly identified, since it here lies under 10 and 11, rising close to 
the fore end of the latter and passing back to the hind end of the former. No. 9 is 
much broader than usual. : 
Nos. 10 and 11 are both present, and offer no peculiarity, except that 11 is expanded 
and sometimes double in front. ; 
Nos. 12, 13 and 14 are absent. 
No. 15 is a straight muscle, longer than, and lying at the side of, 9. - ; 
No. 16 is completely double; in front it lies at the upper side of 17, and under it behind. 
No. 18 rises under the hinder end of 21, and passes forward with a slight inclination 
downward to be inserted at the lower side of the fore end of the same muscle. 
Nos. 19, 20 and 26 are parallel to one another; they rise under 17 and 21, and 
pass forward and upward to be inserted at the anterior end of the segment, not far 
above 16. : 
No. 22 rises under the fore end of 16 and passes backward and upward to the hind 
end of 6. 
Nos. 23, 28, 29 and 34 seem to be absent. 
_ No. 31 is perhaps wrongly identified. It rises under 
In front of the spiracle. 
Nos. 37 and 38 appear to be absent. 
16 and passes upward and forward 
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