There is yet one more organ to which I must draw attention, and that is the curious bag-shaped object marked E.
Just as the silk is contained in the vessel C, so the saliva is contained in E, and is developed according to the character and habits of the insect. Some insects require a large supply of that liquid, which is used for various purposes, and others require comparatively little. The caterpillar in which these receptacles may be found best developed is the larva of the Goat-moth, which may be easily found within the substance of decaying trees. Of the Goat-moth we may speak in a future page.
If the reader will again refer to the engraving on [p. 100], he will see that between the tracheal tube and the digestive apparatus is a curiously waved line, forming two loops in its upper portion, and running into a confused entanglement below. This entanglement, however, is only apparent, for in nature there is no entangling; all is perfect in order.
This wavy line represents one of the numerous thread-like vessels that surround this portion of the digestive apparatus, and are called the biliary vessels, being, in fact, the insect’s liver. There is a large mass of these biliary vessels, and they are found so closely entwined among each other, and so encircled with the air tubes, that to separate them is no easy matter. Their microscopic structure is curious, and will repay a careful examination.
In examining the creature for the first time, the dissector will be tolerably sure to damage the organs and unfit it for preservation, and therefore it is best to take such a course for granted, and to make the best of it.
Removing all these vital organs, he should then examine the wonderful and most complicated muscular structure, by which the caterpillar is enabled to lengthen, shorten, twist, and bend its body in almost any direction, and that with such power that many caterpillars are enabled to stretch themselves horizontally into the air, and there to keep themselves motionless for hours together.
Few people have any idea of the wonders that they will find inside even so lowly a creature as a caterpillar—wonders, too, that only increase in number and beauty the more closely they are examined. When the outer form has been carefully made out, there yet remains the microscopical view, and after that the chemical, in either of which lie hidden innumerable treasures.
A very forcible and unsophisticated opinion was once expressed to me, after I had dissected and explained the anatomy of a silk-worm to an elderly friend. He remained silent for some time, and then uttered disconnected exclamations of astonishment.
I asked him what had so much astonished him.
“Why,” said he, “it’s that caterpillar. It is a new world to me. I always thought that caterpillars were nothing but skin and squash.”