THE SILKWORM ITS INTERNAL STRUCTURE. 



47 



is taken, of course there is no chance 

 of their being refilled ; it is not sur- 

 prising, therefore, that as there is no 

 further use for them, they disappear 

 altogether in the subsequent stages 

 of the insect. Even in the cater- 

 pillar, they are far larger just before 

 spinning the cocoon than at any other 

 time. 



In the moth, too, the nervous 

 ganglia become reduced in number 

 (Fig. 14 a) owing to the fusion of 

 some of them together, and those of 

 the head become very much larger. 

 Very considerable changes also occur 

 in the digestive system; if Fig 16, 

 which represents the digestive system 

 of the moth, be compared with Fig. 

 13, it will be at once manifest that 

 the apparatus has so changed as to 

 be hardly recognisable as the same 

 thing. The gullet has become ex- 

 tremely narrow, and carries a large 

 dilatation, the crop, at its side ; the 

 stomach is much reduced, and would 

 scarcely be recognised but for the 

 delicate malpighian tubules at its junc- 

 tion with the intestines ; and the 

 latter organ itself has become longer 

 and extremely narrow in front, though 

 greatly dilated behind. 



In the foregoing pages we have 

 endeavoured to give a brief outline of 

 the anatomy of our silkworm larva, as 

 it would present itself to one who should 

 proceed to the dissection without any 

 previous knowledge of the subject. To 

 many it will be a matter of surprise that 

 there is so much to be found in the 

 body of a simple caterpillar; but the 

 truth is, that the above is only an ex- 

 ceedingly brief and imperfect description 

 of what is, in reality, an organism of considerable complexity. 

 Any one who is curious to know what can really be made of the 



Fig. 16. Digestive apparatus of 

 Silkworm moth. 



