976 THE AMERICAN NATURALIST. [VorL. XXXV. 
* Augenzahl veránderlich, gewöhnlich mehr als 4; 9 oder 10 
Rüsselnerven; das Rhyncocoelom erstreckt sich nicht bis an 
das Kórperende; die Nephridien dehnen sich von der Gegend 
des Gehirns bis zur hinteren Korperspitze aus; zwitterig, 
ovipar." The species found in the vicinity of Chicago agrees 
with S. græcense in not being protandric, but since I cannot 
find that it differs in other respects from the description given 
by Montgomery of .S. asensoriatum, I am inclined for the pres- 
ent to regard the two as identical. It appears probable, more- 
over, that S. asensoriatum Montgomery is identical with Tetra- 
stemma aquarum dulcium Silliman. In any case the two forms 
are closely allied, as Montgomery admits. 
The species under consideration is a slender worm, attaining 
often a length of 20 mm. (Montgomery gives the maximum 
length as 18 mm.). It varies in color from a light yellowish, 
almost cream-color, in the smaller specimens, to a deep orange- 
red in many of the large individuals. Even in the most bril- 
liantly colored specimens, however, the terminal regions of the 
body are more yellowish than other parts. The reddish colora- 
tion is especially distinct in the nervous system. In many of 
the larger specimens the region of the brain can be distin- 
guished by the naked eye on account of its deeper coloring. 
Individuals in which the eggs are nearly ripe show scarcely a 
trace of the reddish tint, being almost pure yellow in color. 
Animals kept in the laboratory for a long time without food 
usually become more or less brownish, owing to the appear- 
ance of black pigment in the integument. This pigment is 
occasionally found in newly captured specimens. Iam inclined 
to believe that its appearance is connected in some manner 
with the lack of food. 
The usual number of eyes is six, the anterior pair being the 
largest and the posterior pair the smallest. Variation in the 
number of eyes, or at least in the number of pigment spots, 
is of frequent occurrence. Specimens with only four eyes 
sometimes occur, but are rare. In case eight symmetrically 
placed eyes are present, the anterior pair is usually small and 
situated a short distance in front of the largest pair. The 
eyes are very often unsymmetrically placed or differ in number 
