30 TRANSFORMATIONS OF INSECTS. 



perfect insect. These long tubes form the web-spinning apparatus 

 in the larva ; but after the cocoon is finished, and the first trans- 

 formation takes place, not only do they become small, but their 

 function alters. The small glands of the perfect insect secrete 

 saliva instead of web, and assist in digestion. 



In the silkworm the oesophagus is short ; the stomach, a kind 

 of long cylinder, composes the bulk of the digestive apparatus, 

 and the intestine is remarkably limited in its length. But in the 

 moth the oesophagus is long and has a crop ; moreover, the stomach 

 is shorter, whilst the intestine has greatly increased in length, 

 its end being very large and globular. 



If the chrysalis be examined, the gradual passage of the large 

 stomach of the caterpillar into the small organ of the moth can 

 be traced, and also the formation of the crop and the changes in 

 the glands. 



Many larvae get very fat before the chrysalis or pupa condition 

 sets in, and the oily matter collects in the tissue around the digestive 

 organs, and even pushes itself amongst the internal structures of 

 the insect. During the mysterious pupa state this fat disappears, 

 and doubtless it goes to make the beautiful tissues which do not 

 exist in the caterpillar, but which characterise the full grown 

 creature. 



The differences in the blood and its circulation in the larvae 

 and the perfect insects are not satisfactorily determined, but the 

 quantity of the first and the force of the latter evidently diminish 

 in the chrysalis. 



