314 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Antennce . — The dorsal antenna is situated in the striated area, a little back of the constriction 
separating off the head-sheath. The lateral antennae are remarkably nnsymmetrical in their posi- 
tion, recalling the condition found in Rattulus cylindrieus Imhof. The left lateral antenna (fig. 
28, l. a.) is far forward, considerably in advance of the middle of the body, while the right lateral 
antenna is far back, near the base of the foot (fig. 28, r. ci.). 
Foot . — The foot is very slender, conical in form, and so attached to the lorica that it may bend 
to the right, but not to the left. In other words, the posterior part of the body is constructed as 
if it had been twisted over to the left. The position of the toes is likewise such as would be explained 
by siich a twist. 
Toes. — The two toes lie very close together, as a rule, so that in a cursory examination they 
might be taken for one. They are unequal, the right toe being a little shorter than the left. The 
longest toe is about one-third the length of the lorica. In correspondence with the position of the 
foot, as set forth above, the right toe lies with its base above the left, further adding to the difficulty 
of distinguishing the two toes in a dorsal view. This position is such as would be attained by a 
twist of the posterior part of the body to the left, as mentioned in the account of the foot. At the 
base of the toes there are, according to Western (1894) , three small substyles; these I have not been 
able to see. 
Internal organs. — The brain is immensely enlarged, in some specimens extending farther 
backward than the middle of the body and taking up a large share of the space within the lorica 
(see fig. 27, hr.). In such cases the brain can be seen to be made up of large cells, the outlines of 
which can be clearly traced (see the figure just referred to). It is possible that this immense size 
is a transitory condition, not always present. The eye is attached to the dorsal surface of the 
brain, in front of the middle of the latter. In a dorsal view the eye underlies the thickening or 
ridge which runs backward from the base of the left anterior spine (fig. 29) . The trophi are rather 
slender, and are somewhat nnsymmetrical . the left manubrium being much better developed than 
the right (fig. 81). The mucus reservoir is divided longitudinally into two equal halves, one of 
which opens at the base of each toe. The other internal organs call for no special remark. 
Measurements . — Total length, about 0.275 mm. ; length of toes, 0.05 to 0.06 mm.; of anterior 
spines, 0.035 to 0.045 mm. 
Movements. — Diurella stylata Eyferth swims in a rather wide spiral, in an awkward manner. 
The animal continually rotates over to the right as it swims, and at the same time it swerves 
continually toward the side which bears the spines; thus the spiral is produced. 
When suddenly stimulated, as by swimming against an obstacle, or by the striking of some 
other organism against it as it swims, the animal usually reacts as follows: The cilia are partly 
withdrawn and the dorsal spines are bent down a little over the entrance to the lorica. If the 
stimulus is very strong the cilia are completely retracted and the animal remains quiet. If the 
stimulus is not so strong the cilia are only partly retracted and immediately begin operations 
again. But now they act in such a way as to turn the organism toward the side which bears the 
spines. The organism therefore swerves in the direction so indicated. This is, of course, the same 
direction in which the swerving occurs in the usual movement, only after a stimulus the swerving 
is more pronounced, so that the entire course of the animal is changed. For some time after the 
stimulation has occurred the swerving toward the side bearing the spines is much more marked 
than usual, so that the path followed becomes a much wider spiral. 
History. — Diurella stylata, was described by Eyferth in 1878. This description (1885, p. Ill) 
was not clear in its account of the anterior spines, one of which he says arises from the “neck,” 
while he seems to imply that the other rises from the brain. The folds in the anterior edge of the 
lorica he described as “ one or two short spines ” on the ventral side. Otherwise his description is 
good and his figure is at once recognizable as identical with the organism I have described above. 
Western (1893) redescribed this species as Rattulus bicornis. In his first description he described 
and figured the two toes as equal in length, a mistake which he afterward corrected (Western, 
1894, p. 7). Scorikow (1896) described this species as a new one; by a rather curious coincidence 
he selected the same name ( Rattulus bicornis) as Western had done. He also made the same mis- 
take as Western in describing and figuring the two toes as equal. In the same year as Western, 
Wierzejski (1893) described what seems to be the same species under the name Ccelopus similis. 
In Wierzej ski’s figure the two equal anterior spines are shoi’ter than usual, and the body is thicker 
