THE LARGE CABBAGE WHITE BUTTERFLY 185 



in no important respect from the younger larvae, is convenient 

 for examination. It consists of a head and thirteen segments. 

 The head is of a slaty-brown colour with black spots, its under side 

 is yellowish. It is very hard, a firm skeleton being required for 

 the attachment of the muscles which move the mandibles on 

 which so much work falls during larval life. Low down there 

 projects from the front of the head a pair of very short antennae, 

 on each side is a group of five minute " simple " eyes arranged 

 in a curve. A magnifying glass is needed to see these structures. 

 The mandibles, the most conspicuous of the jaws, are hard and 

 horny, and work across from right and left to meet in the middle 

 line. The two pairs of maxillae are too small for detailed treat- 

 ment here. Behind the mouth, projecting from the edge of the 

 lower lip, is a pointed pimple the spinneret from which the silk 

 is exuded in a liquid condition when required. The liquid silk 

 is manufactured in two tubes, one on each side of the body, which 

 open together at the spinneret. In some caterpillars, e.g. the 

 silkworm, these glands are of enormous length, as many as five 

 times the length of the body. It is from these tubes that the 

 " silk-gut " used by anglers is prepared. The hardening of 

 the naturally discharged silk is not merely a process of drying, 

 but rather of coagulation ; a kindred phenomenon is the clotting 

 of blood. There are two other tubes opening close to the mouth ; 

 these come from the salivary glands, and discharge a digestive 

 fluid on to the food as it is being cropped. When handled the 

 larva will often emit, partly from its mouth and perhaps partly 

 from the salivary glands, a greenish fluid of disagreeable odour. 



The thirteen segments composing the rest of the body are all 

 much alike; their general colour is yellowish green with black 

 spots and blotches, but along the middle of the back and on each 

 side at the level of the spiracles is a line of clearer yellow. The 

 whole surface is covered with fine whitish hairs. The first three 

 segments each bear a pair of true jointed legs, ending in a curved 

 claw; the joints are very short and require a magnifying glass 

 for their determination. These three segments form the thorax. 

 The next two segments have no legs of any sort ; the third, fourth, 

 fifth and sixth of the abdomen each have a pair of "false-legs" 

 or " claspers," and there is a fifth pair of claspers of slightly 



