No. 428.] THE METAMORPHOSIS OF SISYRA. 623 
Meinert found similar conditions in Myrmeleon, except that 
there were six tubes with the double attachment and two with 
free ends. He also found that there was no posterior exit 
from the stomach, but that the small intestine (?) had atrophied 
into a compact string of cells with no opening between the 
point of attachment of the silk-secreting tubes. The unassim- 
ilated portion of residuum is expelled as a mass after the insect 
has become an imago. 
In Sisyra, as I have before mentioned, there is no such 
residuum, since the juices of the sponge are ready for com- 
plete absorption. An extensive digestive tract being in this 
way rendered superfluous, nature has economized by modifying a 
large part of the alimentary apparatus into a silk-secreting organ. 
The posterior fourth of the stomach appears merely as a 
solid cord of atrophied cells, which ends in the walls of a 
dilatation, — “silk receptacle," it may be termed. The walls. 
of this receptacle have the structure of those of the Malpighian 
tubules. It appears to be the outlet of five tubules, three of 
which are attached here at both ends, and two of which extend 
posteriorly and end in the body cavity. All are modified in 
their middle portions for the secretion of silk. The cells of 
the silk-secreting portion are much larger and more irregular 
in shape than the ordinary Malpighian tubule cells, and show 
the singular branched nuclei characteristic of silk gland cells 
in the caterpillar and other insects. 
The three tubes having the double attachment proceed 
anteriorly to about the middle of the metathorax and are 
then modified at or near the point of their backward turn. 
Posteriorly they are modified almost immediately after leaving 
the silk receptacle at the base of the stomach. The two tubes 
having the single attachment have a considerable portion of 
unmodified tubule at their distal extremity, intricately coiled 
upon itself, as is shown by the number of variously cut sections 
which appear at this place in any of the three standard planes 
. through the body. The length of the silk-secreting portion is 
increased by complicated coils and turns of the tubes, so that 
they completely fill the body cavity in the first seven abdominal 
Segments, making it next to impossible to accurately trace 
