CHAP, xii BACKBONELESS ANIMALS 



255 



The breathing is effected by means of the numerous 

 air-tubes or tracheae which open externally on the sides 

 and send branches to every corner of the body. As the 

 air is thus taken to all the tissues, the blood- vascular 

 system has little definitcness, though there is (as in other 



H 



in 



H. i 



FIG. 76. THE LARGE CATERPILLAR OF A SPHINGID MOTET, NATURAL SIZE. 



The student will find it a profitable practical exercise to make a careful 

 study of the external features of a large caterpillar. The head consists 

 of a 'number of fused segments, in great part enclosed in two large epi- 

 cranial plates, which bear half a dozen pairs of simple eyes (). 

 Between the epicranial plates in front is a triangular clypeus, which bears 

 the upper lip or labrum. Posterior to the labrum are two strong mandibles. 

 Behind the mouth the first and second maxillre have united in a lobed 

 plate. The antennae (A) are three-jointed, but very small. 



It is interesting to contrast the head of the caterpillar with the head of 

 the moth, e.g. the minute antennae with the long antennae, the simple eyes 

 with the compound eyes, the strong mandibles with the vestigial mandibles. 



Behind the head are thirteen segments with a much softer cuticle. The 

 first three correspond to the thorax of the adult and each bears (I, II, III) 

 a pair of five-jointed clawed legs, which correspond to the legs of the 

 adult. The first segment bears two breathing apertures or stigmata, 

 which are not present in this segment of the adult. 



On the region corresponding to the abdomen there are eight pairs of 

 stigmata (ST) leading into the air-tubes or tracheae. The eighth abdo- 

 minal segment bears a curious dorsal horn (H), the ninth segment is in- 

 conspicuous externally, having been in part telescoped. Setae and pigment 

 spots are seen on the cuticle. 



The first two abdominal segments have no appendages. The next 

 four have unjointed, unclawed " pro-legs," with a chitinous gripping plate. 

 The first is marked by the figure 1. There are no appendages on segments 

 7, 8, 9. On the last,' the tenth, there is a pair of anal pro-legs, marked 5. 



