324 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
ticula forward a<xain on the ventral side as far as the brain. They 
send out no branches, however, on the ventral side of the animal. 
The median, larger portion, into which the lateral branches con¬ 
nect by the cross tube, must unite in some way, just back of the 
uterus in the female and the seminal vesicles in the male, to the 
large sac, which is not seen in the youngest specimens and which in 
all adults is full of purple-edged, whitish globules. This I have 
called the renal sac. Just before the renal sac is reached there are 
two tubes given off at an angle toward the posterior end of the 
animal. As soon as these tubes reach diverticula 2a and 2d of the 
alimentary canal they follow these diverticula to the posterior end 
and stop blindly as they reach the region where the intestines turn 
forward. 
Behind the spot where the median tube connects with the renal 
sac it bifurcates and each section passes back to the posterior of the 
animal, follows the body wall to the ventral side, then forward again 
to the region of the ventral end of the renal sac, and each turns out- 
ward and ends blindly. 
A section across a Malpighian tubule has been shown with that 
of an intestine diverticulum and a trachea in fig. 12 (pi. 20). There 
is a very faint, often imperceptible connective tissue layer on the 
outside. The renal cells are flat with comparatively large nuclei. 
This differs from the condition in Ixodes only in the comparative 
size of the nuclei. Pagenstecber says that the nuclei in the renal 
epithelium are small. 
In the older specimens, both male and female, the renal sac and 
later (pi. 22, fig. 22), the different branches of the excretory system 
are filled with the opaque, purple-edged globules previously men¬ 
tioned. These globules, according to both Pagenstecher and Grif¬ 
fith, give the murexide test for uric acid, thus proving the renal 
function of the system. No clear connection with the outside of the 
body has been demonstrated. The observed relation of the renal 
sac to the postintestine is represented in fig. 7 (pi. 19). There may 
be a free passage in younger specimens, but the steady accumulation 
of renal material throughout life and the definite order of filling the 
renal cavities with the renal globules indicates that there is no real 
amount of excretion. 
In a young female the renal tubes are either invisible or visible 
because outlined by pigment about their walls. In an older tick 
