At Fig. 18 the interior parts are more particularly exhibited. a, the circle from which many vessels originate; b, the thorax or breast, joined to the head by the neck, c; the part which is supposed to be the heart is plainly seen at d; the abdomen, f, is separated from the breast by a ring, e; g, the tail.
Fig. 19 exhibits the animal not fully extended, though with its wheels in motion.
Fig. 20 shews it with its side towards the eye; in this position one of the wheels, a, appears to lie considerably below the other.
Fig. 6 and 16 represent two of these creatures in the postures in which they are frequently seen when the wheels are not protruded, but with the fibrillæ, a b, vibrating quickly.
Fig. 2 exhibits the animal with the body nearly drawn into the abdomen; at Fig. 21, the body still further drawn in; at Fig. 22, as it appears with the tail partly drawn in; at Fig. 23, in a globular form, but still adhering by the tail.
Sometimes, when in the maggot form, it rolls its head and tail together, without drawing them into the body; as represented at Fig. 14.
Baker has also described three other species, one of which, differing only from the preceding in having a very long tail, is represented at Fig. 7.
Fig. 11 is another kind, with crustaceous spiculæ, b, at the fore-part; within this, at c, an opake oval body may be seen, which has been taken for an egg.
Fig. 3 is another kind; it has two projecting points, a a, from the tail, and the head furnished with a number of fibrillæ, b b.
Fig. 13 represents another species, described by Spallanzani.