like nicely-pointed paint brushes, but when the animal is compressed
they quickly become fibrillated, and then look like extremely old and
worn brushes. These cirri are placed in depressions in the ventral
surface and each one appears to come from a specific shoulder. At the
posterior end an oblique hollow bears 6 unequal cirri placed side
by side. The extreme right cirrus is the largest, and they become
progressively smaller to the opposite end. Dorsal to these lies the
contractile vacuole. The peristome is in the posterior half of the
body and an undulating membrane extends from it into the oesophagus.
The dorsal surface is longitudinally striated by 5 or 6 lines, which
are usually curved. The nucleus is horseshoe-shaped and lies in the
posterior half of the body. Length 68µ; diameter 48µ.


[Illustration: Fig. 56.--_Aspidisca hexeris_.]


This form was incorrectly mentioned as _Mesodinium_ sp. by Peck '95:

In the figure given by Quennerstedt there are only 7 ventral cirri.
In the Woods Hole form there are 8, 7 of which are anterior, 6 of
them about one central one. The eighth cirrus is by itself, near the
base of the largest posterior cirrus. These cirri, in spite of their
size, are easily overlooked and more easily confused, but by using
methylene blue they can be seen and counted.


Aspidisca polystyla Stein. Fig. 57.

This species is similar to _A. hexeris_, but is smaller, very