OF THE LARVA OF PYGÆRA BUCEPHALA. 183 
just above the upper end of 46, and passing downward is inserted just below the lower 
end of 53. : 
No. 52 is absent. 
No. 55 is single in the sixth segment. 
Nos. 16 and 17 approach nearer to one another, and separate a little from 18. 
Nos. 47 and 48 are absent. 
No. 49 in the fifth and sixth segments is completely double, and stronger than in the 
fourth segment, which indicates that the prolegs of these segments act in a somewhat 
different manner. 
The gastric muscle ç rises, as in the larva of Cossus, on the upper side of 21. 
Seventh Abdominal Segment.—Owing no doubt principally to the absence of prolegs, 
this segment differs much from those that immediately precede it. Thus 47, 48 and 56 
are entirely absent. 49 and 50 also, though present and well-developed, are much shorter 
than usual. — 
On the other hand, in the specimens I examined there were two new muscles lying 
under 10 and 11, and inserted below them in front. 10 and 11 approach one another in 
front, and sometimes even unite together. 
No. 25 has completely united with 24, and 26 lies on the lower side of these two muscles. 
To represent 31, 32, 57 and 58, there are four small variable muscles which seem to be 
of little importance. 
No. 46 also is very thin and weak, so that it is probably of little functional utility, and 
only present to fulfil the general law of arrangement of the muscles. 
No. 51 is single and small. It rises at the lower end of 49 and passes to the front of 
34, as in the anterior abdominal segments. 
No. 52 is absent. 
No. 53 is parallel and similar to 54, though a little shorter; these two muscles are very 
unlike in front, but become gradually more and more alike. 3 
No. 56. As there are no prolegs to this segment, the series of muscles marked 56 is 
absent, 
Nos. 57 and 58 are represented by two small muscles parallel and similar to 31 and 32. 
Eighth Abdominal Segment.—In this segment the muscles have become much narrower 
and weaker, and 31, 32, 33, 34, 50, 53 and 56 are absent. 
. Nos. 12 and 13 have almost coalesced, so as to form one small muscle, and the same 
has taken place with 14 and 15. i ne 
No. 4 has entirely disappeared, while 3, on the other hand, is double; as also happens 
in the larva of Cossus. re 
Nos. 7, 8, 10 and 11 have become parallel, and seem to form ee: war 
In the Ninth Abdominal Segment the diminution of the muscles in size and num! en = 
proceeded still further; 3, however, is double, as in the preceding segment, gn ar 
its appearance again. A 
Indeed the DEG of missing muscles is much greater than of those which are pre- 
sent. These are, Nos. 1, 2, 3, 4, 5, 6, 7, 16, 17, 18, 21, 37, 38, 50 and Ble 
The first six of them resemble the same muscles in the preceding segment. 
