184 MR. LUBBOCK ON THE CUTANEOUS MUSCLES 



No. 7 rises at the posterior end of 16, and passes forward and upward nearly to the 

 upper end of 37. 



Nos. 16 and 17 have coalesced. 



Nos. 50 and 51 are even larger than usual, and pass quite back to the posterior end of 

 the segment. 51 is double in front and attached under 16. 



Besides these muscles, there are attached to the upright wall of the end of the body, 

 and in a series along the lower middle line of the segment, a number of muscular fascicles 

 which are distributed to the rectum and posterior parts of the alimentary canal ; in the 

 same place also are situated the muscles which move the posterior prologs ; I have not, 

 however, examined these muscles with care enough to enable me to describe them satis- 

 factorily. 



Comparison of the Muscles in different Specimens. — Any one who has carefully exa- 

 mined Lyonet's drawings of the cutaneous muscles in the larva of Cossus ligniperda, or 

 stni better, has made himself acquainted with the organs themselves, must have been 

 struck with amazement at their number and complicated arrangement. 



The muscles in most animals are penetrated by the arteries and capillaries, and are 

 supplied by them with blood ; but this not being the case in insects, it is perhaps neces- 

 sary that their muscles should be divided into numerous fascicles, in order that the blood 

 may have free access to them. Whether for this or some other reason, they are in the 

 shape of thin ribands, the thiclcness of which varies very much in different muscles and 

 in different parts of the same muscle, but is in the largest about -o^th of an inch. 



The largest mtiscidar fibres in man, which are not penetrated by blood-vessels, are, I 

 am informed by Professor Huxley, 4^th of an inch in diameter. We can, however, 

 derive no argument from this comparison without knowing the permeability of the muscle 

 and the power of penetration possessed by the blood. It is also worthy of notice, that the 

 wing-muscles of insects are separated into very small fascicles, as if, from the violent and 

 rapid action of these muscles, their particles were more quickly deteriorated, and required 

 therefore more frequently to be removed and replaced by others. The muscles of 

 insects, however, are not only very much divided, but are also very complicated in their 

 arrangement. 



Lyonet describes 1647 in the larva of Cossus, without counting those which belong to 

 the head and to the internal organs ; and truly observes, that this great number " ne 

 pourra qu'etonner ceux qui savent qu'on ne fait ordinairement monter tons les muscles 

 de rhomme qu'a 529, et qu'il y en a meme qui le fixent k beaucoup moias." It might 

 be objected, that certain fascicles in insect larvae, as for instance 16, 17, 18, 19 and 20, 

 ought to be considered as parts of muscles rather than as whole muscles, and that the 

 total number therefore must be very much diminished. 



If, however, tliis were a well-founded objection, we should expect to find these fascicles 

 varying in relative size and number; and as, except in certain instances, they do not 

 do so, we must, I think, admit that Lyonet was right in his mode of estimating their 

 number. 



Some few, however, of the smaller muscles do vary ; and to determine the number and 

 amount of these variations was my chief object in undertaking the present paper. 



