Development and Metamorphosis 



39 



The eggs have been laid, because of the remarkable instinct of the 

 mother, in a situation determined chiefly by the interests of the young 

 which are to hatch from them. The young of many kinds of insects take 

 very different food from that of the mother a caterpillar feeds on green 

 leaves, the butterfly on flower-nectar or live under very different circum- 

 stances young dragon-flies and May-flies live under water, the adults in 

 the air. A monarch butterfly, which does not feed on leaves, nor has ever 

 before produced young, seeks out a milkweed to lay its eggs upon. The 

 young monarchs, tiny black-and-white-banded caterpillars, feed on the 



FIG. 69. Early stages in the development of the egg of saw-fly, Hylotoma beriberidis. 

 C, ventral plate removed from egg; D, ventral plate, showing segmentation of body; 

 E, embryo, showing developing appendages; F, same stage, lateral aspect; G, older 

 stage, lateral aspect, ant., antenna; md., mandible; mx., maxilla; li., labium; /', P, / 3 , 

 legs; sg., salivary glands; St., spiracles; ab.ap., abdominal appendages; n.c., nerve- 

 centers; a., anal opening; lb., labrum; sd., cesophageal invagination; y., yolk; 

 b.s., abdominal segments; pd., intestinal invagination; am., amnion; s., serosa. 

 (After Graber; greatly magnified.) 



green milkweed leaf-tissue; indeed they starve to death if they cannot have 

 leaves of precisely this kind of plant! The reason that the butterfly, whose 

 only food is the nectar of almost any kind of flower, ranges wide to find a 

 milkweed for its eggs, is one not founded on experience or teaching or rea- 

 son, but on an inherited instinct, which is as truly and as importantly an 

 attribute of this particular species of butterfly as its characteristic color 

 pattern or body structure. And the female of the great flashing strong- 

 winged dragon-fly, queen insect of the air, when egg-laying time comes, 

 feels a strange irresistible demand to get these eggs into water, dropping 

 them in from its airy height, or swooping down to touch the tip of the abdo- 



