186 MR. LUBBOCK ON THE CUTANEOUS MUSCLES 



31, 32, 33, 34 ; and 40, 41 and 42 ; then the variations ohserved in these muscles will be 

 of very little importance to the animal. 



There are, indeed, other muscles and series of muscles which might a priori have been 

 considered equally unimportant, and have therefore been expected to show similar varia- 

 tions. Our knowledge, however, of the mechanism of the muscles, and of the functions 

 they subserve, is so small, that we must be very cautious in forming an opinion on the 

 relative importance of different muscles. 



It may perhaps prove that the variability of particular muscles is rather an indication 

 of a different arrangement hereafter to be discovered in certain neighbouring groups. 

 We must, however, suspend our judgment upon these facts until we are better acquainted 

 with the myology of other insect larvae. 



I expected to find, in specimens in which the variable muscles were divided into more 

 fascicles than usual, that this tendency to the division of muscles would pervade the 

 whole animal, or at least the whole segment ; this, however, did not appear to be at all 

 the case. It seemed also probable that the variable muscle would either be symmetrical, 

 or at least would tend to be so, in the two opposite sides of the same animal ; but in the 

 instances in which both sides were examined, this rule was not found to hold good. 



Differences in the Third Abdominal Segment. — In the fourth specimen. No. 1 sends 

 off a small branch on the dorsal side at the front end. 



No. 5, in the sixth specimen, is partly overlapped by 4 in front. 



The series 12 to 15 consists normally of four small muscles sitviated in the hinder part 

 of tlie segment, and passing forward with a slight inclination downward. However, in 

 the third specimen which I examined, the fore end of 15 was turned under 14. No. 12 

 was double in front, and 13 was almost entirely double, being only joined together in 

 front. In the fourth specimen 13 and 14 were completely double, and 12 and 15 were 

 divided for the anterior portion. The two branches of No. 15 were unequal, the dorsal 

 one being the longer, and inserted under the anterior end of 14. In the fifth specimen, 

 12, 13, 14 and 15 were double in front. In the sixth and eighth specimens, on the con- 

 trary, 12 and 13 were united together ; and in the latter are shorter than, in the former 

 the same length as, 14 and 15. 



No. 7 is usually single, but in one specimen it was divided into two, for about the 

 posterior one-third. 



No. 20, in the sixth specimen, a little overlapped 19 in front. 



No. 22 is usually double for about its anterior half; sometimes, however, it is more 

 deeply cleft, and at others it is almost undivided. Sometimes again it is trifid, and in 

 this case the three divisions may differ in size and in degree of division. 



No. 25 varies a good deal in width in different specimens. 



Nos. 28, 29 and 30 also vary a good deal. Sometimes all three are of about the same 

 width. Sometimes 28 is much the largest, and is bifid, trifid, or even quadrifid. At 

 others 28 is smaller than 29, and the latter is more or less bifid or trifid. Sometimes 

 both these muscles are bifid, and in one instance 30 was completely double. 



Nos. 31, 32, 33 and 34. Sometimes 31, sometimes 32, sometimes 34, is double ; some- 

 times both 31 and 34 are double. Sometimes, on the contrary, 33 and 34 have coalesced. 



