776 Wisconsin Academy of Sciences, Arts, and Letters. 
cuticular lining (fig. 38). Muscles are inserted on either side 
at the opening of the duct on the hypopharynx. 
Malpighian Tubules. 
In a general dissection of Libellula 4,-maculaia the Mal¬ 
pighian tubules are seen to arise from the intestine near the 
posterior end of the seventh segment; from here they all ex¬ 
tend backward and lie principally in the eighth and ninth ab¬ 
dominal segments, seldom extending hack into the tenth. In 
the ninth segment some of the tubules bend and run forward 
again but not beyond their point of union with the intestine. 
The ileum is covered with the tubules and they are in general 
more numerous here than over the rectum. 
An examination of the union of , the tubules with the in¬ 
testine shows that they do not open into it singly hut that sev¬ 
eral tubules unite to form a common vestibule which opens at 
the boundary of mid-and hind-intestines.' The number of these 
openings varied in the specimens in which they were counted, 
there being from eighteen to twenty-two; the number of Mal¬ 
pighian tubules uniting for a common opening varies from two 
to twelve, the average was 8.25. 
The minute structures of the tubules is similar to what has 
been found in other insects. The different tubules are similar as 
to size and structure or, if variations do occur, they are only 
what might he expected from an examination of a great number 
of sections and surface views. In the vestibule and in the 
tubules just before opening into it, the epithelial cells are smal¬ 
ler than in other parts. A few of the tubules showed an ab¬ 
normality in that they-were very short with swollen ends, in 
which part the wall was somewhat thinner than usual and the 
lumen much larger. 
The lumen of the tubules is very irregular and, examining a 
number of specimens, one often sees in a single tubule that the 
lumen changes in diameter. An examination of transverse sec¬ 
tions also showed this variation in size of the lumen and that 
it was always irregular and angular. Griffith (12) noticed this 
