TIIK CATKltlMI.LAi:: IXTKUXAL OIKIAXS. 17 



of a li\inLi- creature, we shall first consider the muscular system, through 

 which the framework and its appendages are moved ; next we sliall take up 

 the digestive system, the province of" which is to prepare crude nutriment for 

 the insect ; the further preparation of this nutriment by oxygenation 

 re(|uires that we should follow with the respiratory system ; and the distri:- 

 hution of the nutriment over the body by the circulatory system completes 

 the circuit of the relation of food to the creature ; but whether the natural 

 action of these systems be voluntary, as in the first mentioned, partly 

 voluntary and partly involuntary, as in the second, or Avholly involuntary, 

 as in the last two, they all require to be brought into relation to the will of 

 the animal, or their vital action ceases ; we shall therefore consider next the 

 nervous system, the seat of volition and sensation. We shall follow this 

 with the glandular or secretory system, since its sole independent re[)resen- 

 tative is the organ which serves to secrete silk, by means of which the 

 caterpillar is able to walk where it needs to procure nourishment. These 

 are all the systems \\-hich liaAC to do simply with the life of the individual, 

 but there is still another, the reproductive, which must take the highest 

 place as related to the life of the species ; though in the caterpillar this 

 remains in an embryonic condition, a condition of preparation for future 

 development ; and finally we shall consider briefly the cellular system, 

 whose extreme development is confined to the larval stage and is intimately 

 related to all the other systems. 



Muscular system. The muscular system of caterpillars consists almost 

 entirely of fiat ribbons of simple muscular fibre. For convenience sake, 

 and also to a limited extent as a natural classification, they may be divided 

 into those occurring in the head and those confined to the body. 



The head is mostly filled with conical muscular bundles, attached by 

 their bases to the upper and lateral portions of the posterior two-thirds, 

 and to some extent to the upper portion of the anterior third of the vault 

 of the head ; the apices of these conical masses converge toward the middle 

 longitudinal line of each hemisphere, and then pass downward, terminating, 

 in the lower half of the head, in a Avhite, glistening, tendinous cord, lying 

 just behind the optic nerve and reaching down into the mandibles, which 

 they serve to close. The extensors of the mandibles are attached behind 

 and below the ocelli, and pass directly to the outer base of the mandibles, 

 which they enter by means of a tendon attached to the interior wall of the 

 same. The retractors of the labrum arc slight, flat, nuiscular ribljons, 

 attached at one extremity along the whole of its upj)er interior edge and at 

 the other to the facial triangle ; the lal)rum is draA\n inwards by a double 

 muscle, which starts above from its attachment along each side of the 

 median suture above the facial triangle, and passes freely downwards, the 

 muscles of the two sides confluent, diminishing in breadth downward, and 

 terminating; in a sino^le tendon attached to the middle of the labrum. 



