Earring and Myers—The Rotifers of Wisconsin. 611 
ricle-like areas of strongly developed cilia; the buccal field is 
closely set with short cilia. 
The mastax is of a remarkable type and without any parallel 
among known species of rotifers. The normal apparatus for 
seizing or triturating the food, the trophi, has in this instance 
become very nearly, if not completely, atrophied, and its func¬ 
tions taken over by a pair of ‘ 1 pseudunci ’ These have appar¬ 
ently been developed from the secondary epipharyngeal structures, 
which are frequently present in the Notommatoid mastax, but 
always in a very subordinate role: to spread the mouth open, as 
in the forcipate type, or to support the anterior region of the 
head during the pumping action, as in Madia. The large, hooked 
pseudunci are expanded at their posterior ends into broad lami¬ 
nae, which are imbedded in the walls of the buccal canal. When 
at rest the points meet at a right angle, with the apex dorsal, and 
protrude slightly through the mouth. The trophi are relatively 
large, but the various parts are very feebly developed; they lie 
obliquely in the buccal canal, with the fulcrum directed toward 
the mouth. The fulcrum is long, rod-shaped, and divided for 
more than half its length. The rami are elongate and rather 
narrow, gradually attenuated toward the tips, and imbedded in 
the soft parts of the mastax; they do not appear to possess either 
abductor or adductor muscles. The left uncus has five, and the 
right four, long, linear teeth, united by a very thin, membranous 
basal plate. The manubria are heart-shaped. The action of the 
mastax has not been studied in the living animal, but from its 
structure it is not unreasonable to assume that the trophi are 
capable of making a partial revolution around a transverse axis, 
as in AsplancJma, which at the same time thrusts the pseudunci 
out through the mouth, brings their points into the same plane, 
and spreads them apart. This could all be accomplished by re¬ 
latively simple muscular arrangements. It would be necessary to 
effect an inward movement of the external edges of the basal 
plates of the pseudunci, which are connected to the bases of the 
rami, in order to bring the points into the plane of the rami; 
continuing the turning movement in this plane would open the 
pseudunci. A pair of adductor muscles attached to the rami 
near mid-length would be sufficient to bring this about. 
The oesophagus is short. The walls of the stomach are crowded 
with symbiotic zoochlorellae, and, as is usually the case among 
rotifers sharing this relationship, no gastric glands are present, 
