174 



the silk glands, becomes perceptibly re- 

 duced in size. It has been estimated that 

 the larva, in attaching the continuous 

 thread of its cocoon, makes two hundred 

 and fifty-four thousand back and forward 

 movements. The cocoons are very 

 strong and dense, of a dirty white color 

 and generally coated with a white pow- 

 der, the female being the larger. 



There is but a single brood in the 

 north, while in the south there are two. 



In order to see if the pupa needed air, 

 Mr. Trovelot sealed up some cocoons 

 over winter in shellac, but the moths 

 emerged in due time after being in an air- 

 tight space for nine months. He also de- 

 layed the emergence of the moth till 

 twenty-one months after entering the 

 cocoon by placing it upon i'ce. 



The silk in the spinning glands before 

 it is spun is a clear, transparent fluid. 

 These glands seem to be of excessive size 

 when compared with that of the larva, 

 since, when fully expanded, they reach 

 the great length of twenty-five inches, or 

 about eight times the length of the full- 

 grown larva. These glands are paired, 

 one being found on each side of the body, 

 are considerably folded and taper at each 

 end. The ducts leading from the anterior 

 end of the glands unite to form a single 

 duct which opens below the mouth. The 

 thread. is double, being really composed 

 of two different fibres, one from each 

 gland, as may be shown by separating 

 them. The silk in these glands is pre- 

 pared and sold as silk "gut" to anglers. 

 On account of its transparency when in 

 water, it becomes invisible and thus aids 

 in deluding the wary fish, who does not 

 see any connection between the line and 

 the baited hook. The "gut" is prepared 

 as follows : Larvae which are ready to 

 spin their cocoons are cut open and 

 placed in strong vinegar for eighteen 

 hours ; the glands are then taken out, 

 stretched and dried in the shade. 



Six or eight days after beginning the 

 cocoon, the larval skin is moulted and the 

 real chrysalic or pupal stage begins. This 

 stage normally lasts till the following 

 spring or summer. A few days before 

 the time of emergence a pair of glands 

 which open into the mouth become very 

 active and secrete an acidulated fluid 



which escapes and wets the fore end of 

 the cocoon, causing the resinous material 

 binding together the fibres to become 

 soft. Even cocoons sealed up in shellac 

 and starch have been dissolved by this 

 fluid, and thus the moths have been able 

 to escape. When the cocoon has become 

 sufificiently soft, the moth pushes its way 

 between the fibres, but in doing so often 

 breaks some of the threads, thus making 

 the silk of such cocoons useless for com- 

 mercial purposes. The moth at the time 

 of emergence, with its folded and crum- 

 pled wings, is quite a forlong-looking ob- 

 ject. These wilted wings soon begin to 

 fill up with fluids from the body, which 

 is very large at this time. In some cases, 

 the fluid is driven into the wings with so 

 much force that they swell up, and if such 

 a wing is punctured, thus allowing some 

 of the fluid to escape, the mature wing 

 will be of a smaller size than one from 

 which no fluid has been lost. It must be 

 remembered that it is possible to inflate a 

 butterfly or moth's wing, because the 

 wings of insects are not composed of a 

 single layer, but are sacs of two layers 

 which are closely applied. It is thus pos- 

 sible to split the wing into upper and 

 lower halves, but this can only be done at 

 the time of emergence, when these two 

 layers are not so firmly cemented togeth- 

 er as they are in a few hours after emer- 

 gence. 



The enemies of Polyphemus are nu- 

 merous. Birds prey upon the larvae, in 

 addition to numerous parasitic insects 

 which are very similar to those which de- 

 stroy Cecropia. The cocoon itself is not 

 a complete protection because rats and 

 squirrels plunder them. We thus see 

 that the life of even an insect is full of 

 dangers, and that it is really a wonder 

 that so many are able to become mature 

 and reproduce. 



The silk-worm moths are excellent il- 

 lustrations of what is called complete 

 metamorphosis in insects. An insect like 

 the grasshopper, when it hatches from 

 the egg, is very much like the adult in- 

 sect in its general form and appearance; 

 the most evident difference being the lack 

 of wings. An insect which shows such 

 slight changes in its growth to maturity 

 is said to have an incomplete metamor- 



