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. 
