THE SILKWORM ITS FORM AND LIFE HISTORY. 19 



At first sight it seems to be situated on the last segment, but 

 closer examination shows that it is really on the last but one. 

 This horn reminds us of a similar and more prominent appendage 

 in the caterpillars of the hawk-moths, which are not very distantly 

 related to our insect. 



Its second age is now entered upon. The period of unavoid- 

 able fast has to be made up for, and the pangs of hunger prompt 

 the newly arrayed grub to seek again its favourite food. This it 

 soon does full justice to, with a result similar to that of its first 

 age, rapidly increasing size and paling colour. This age does not 

 last quite so long as the first, for, about four or five days after the 

 completion of the first moult, the time for the second comes round. 

 This is accomplished in a similar way to the preceding, and the 

 third age is (Fig. 4) entered upon. Again we notice an increased 



Fig. 4. Silkworm Third age. 



Fig 5. Silkworm Fourth age. 



size, and a paler colour, and by this time we can pretty easily detect 

 some curious markings, on different parts of the body ; on the 

 front of the second segment there is a dark line with generally a 

 small, dark spot on each side of it ; on the fifth there are two 

 dark, crescentic marks ; and on the eighth, there are two raised, 

 dark spots. The horn at the hinder end of the body is also a 

 more prominent object. The third and fourth ages (Figs. 4 and 5) 

 last from five to six days each, and during this time the caterpillar 

 increases very considerably in size, and becomes much paler. 



The period of the fourth moult is an unusually trying one, and 

 not unfrequently individuals perish through their inability to 



Fig. 6. Full-grown Silkworm. 



struggle through it. When this moult is over, the animal is very 

 large, and of an extremely pale and sickly-looking colour. Fig. 6 

 represents the animal towards the close of this age, when it is full 

 grown. 



