6o INJURIOUS AND USEFUL INSECTS 



quite unlike anything that has been seen in the larva. All 

 these appendages are movable, though enclosed in a trans- 

 parent envelope, or pupa-skin, and for a short time the 

 pupa is a free-limbed pupa. In the act of extrication or 

 immediately after, the appendages bend forwards, and are 

 arranged with perfect symmetry upon the sides and ventral 

 surface. Then a fluid, which is probably chitinous, though 

 it resembles varnish, exudes from the body, and glues down 

 all the appendages. The pupa becomes agglutinate, and 

 until the moth escapes from its close-fitting and rigid envelope, 

 only the most limited movement is possible. It is not true, 

 therefore, though many books and teachers continue to repeat 

 the statement, that the body of the moth forms during the 

 pupal stage. Externally, at least, it is complete when the 

 pupal stage begins. But the muscles which actuate the new 

 organs are still very imperfect, and many other details of 

 structure have to be acquired before the winged imago is fit 

 for its brief but active career. Sections through an early pupa 

 show that much of the interior is occupied by a nearly fluid, 

 cellular pulp, in which the rudiments of many essential organs 

 can only be made out by microscopic study. 



Even before the pupa frees itself from the larval skin the 

 most characteristic organs of the moth can be distinguished. 

 Take a fall-fed larva, kill and harden it by dipping it for a 

 moment in boiling water, and then strip off" the outer skin. 

 There will be found beneath it the wings and legs, the feelers 

 and mouth-organs of the fly. The change of the crawling 

 caterpillar into a flying moth is prepared long in advance, and 

 the minute rudiments of the new organs can be detected by 

 refined methods of inquiry long before the feeding-stage comes 

 to an end. 



With the larva, pupa, and imago of the tiger-moth before us, 

 we can remark the points of external structure which distinguish 

 each stage of a Lepidopterous insect. The larva has been 

 described in Lesson 12 (p. 51). In the pupa we can make out 

 with some attention the head, which is bent down along the 

 ventral side of the body. The proboscis is stretched out along 

 the middle Hne, and can be seen to be composed of lateral 

 halves ; a pair of pointed projections, touching one another 

 along the middle line, are the labial palps. On either side of 

 the proboscis two legs appear ; then comes the feeler ; the hind 



