THE NATURE OF METAMORPHOSIS. 59 
changes in the larve of the wild bee, Axthophora retusa, but have 
been unable to observe them, although we believe they do really 
occur. But the universally acknowledged accuracy of most of 
Swammerdam’s observations, supported as they are in this instance 
by analogy, fully warrants us in considering this subject as still 
open for inquiry. 
“When a full-grown larva is preparing to change into the pupa 
state, it becomes exceedingly restless, ceases to eat, and diminishes 
much in weight. Many species spin for themselves a covering of 
silk termed a cocoon, or case, in which they await their trans- 
formation. Others prepare little cavities in the earth, and line 
them with silk for the same purpose; and some suspend them- 
selves by their hindermost legs to the under surface of a leaf. In 
each of these instances this important change takes place in the 
same manner. Before the larva thus prepares itself for metamor- 
phosis, its alimentary canal is completely evacuated of its contents ; 
its body, as at the previous changes of skin, becomes dry and 
shrivelled, and much contracted in length; and certain enlarge- 
ments at the sides of the anterior segments indicate the now 
rapidly developing parts of the future pupa. These changes take 
place in all insects in a similar manner, but have been most 
frequently watched in the Lepidoptera, upon which also our own 
observations have been made. We have also observed the same 
changes in the Hymenoptera. 
“The larva of the Sphinx, when it is ready to undergo its 
changes, penetrates the earth to the depth of a few inches, and 
there forms for itself a little chamber, in which it awaits its trans- 
formation. But the larva of the butterfly either fastens itself by 
a little rope of silk carried across its thorax to the under-surface 
of some object, as a ceiling, &c., or suspends itself vertically by 
its hind legs, with its head directed downwards, as is the case with 
the common nettle butterfly, Vanessa urtice. We have watched 
the changes with much care in this insect, which frequently remains 
thus suspended for more than ten or twenty hours before the trans- 
formation takes place. During this time the four anterior segments 
of the larva become greatly enlarged. Then the segments assume 
a curved direction, occasioned by the contraction or shortening of 
those muscles of their under-surface which are repeatedly slowly 
