swam backwards and forwards. No special membrane appears to bound the walls of the long canal.

The nucleus in all the green individuals of this species, which are not engaged in the process of reproduction, exhibits a variable but never large number of rounded segments, strung together like a rose-wreath, lying on the ventral side in the front part of the body, curved more or less sharply from the front and right to the back and left. Stein considers this form of nucleus as decidedly characteristic of the species (S. polymorphus), and would only admit into it such colourless members as conform to this description. S. Mülleri is, however, the only one of the group corresponding in size with polymorphus.

Most frequently he has found the nucleus to consist of from eleven to thirteen divisions. Eight or nine have been found next in frequency, fifteen or sixteen are rare, and in one case twenty were found. Fewer than four divisions he has not seen, five and six very seldom, but seven more often. The number of the nucleus divisions stands in no relation to the age or size of the creature. In very large specimens he has frequently met with only eight or nine, or even six, while very little ones had from thirteen to fifteen. The aspect of the nucleus is shown in Plate I., Fig. 1, n, and Fig. 5.* The nucleus beads, round, or spindle-shaped, usually hang together by short, narrow threads (Figs. 4, 5, 6, 7, 8, 9), but sometimes the connections are thicker, though the beads are always well separated. Sometimes the hindmost beads show a gradual increase in size as compared with those in front, but the first is frequently bigger than those below. Frequently one or other bead in the row will be lengthened und in process of cross-division, or actually divided into two segments (see Plate I., Fig. 7).

Stein twice met with, what he considers, a "monstrous" nucleus, with a branch, as shown in Fig. 5, composed of two or three lateral beads, and he considered that this resulted from a longitudinal instead of a transverse division. On what he deemed a very fortunate occasion he encountered a wounded specimen, with a nucleus, having eleven beads, of the character shown in Fig. 6, with a distinct, opaque, central nucleolus (kerne) in each, mostly including a larger or smaller white spot. The whole nucleus looked like a row of eggs one behind the other, the central "kernel" passing for a yelk vesicle. In other cases Stein found these Stentors with nuclei, in which the beads did not exhibit any nucleoli, but only homogeneous masses. At times one or more beads contained The branching beads from the main line are unusual-see below.

very small nucleoli, without any of the vacuoles shown in Fig. 6. In Fig. 4 a number of small nucleoli are depicted; and in certain individuals, while most of the beads were of this pattern, some had only two or three, or four of the little granules. In Fig. 6 the upper bead shows a nucleolus with four-cornered vacuoles, the second has long unequal nucleoli, each with a vacuole, and the third a large nucleolus with three little vacuoles. Fig. 7 shows, first, a bead dividing; the second bead has an oval nucleolus,* with three transverse vacuoles; and the third a chaplet-shaped nucleolus with seven transverse vacuoles one under the other. Fig. 8 shows a bead with four solid "kernels," and below it another bead, in which the nucleus membrane has been acted upon by acetic acid.

All the Stentors of this species (polymorphus) resemble each other pretty closely in size. Very small individuals, with chapletshaped nucleus are met with. When young the S. polymorphus is always colourless, and furnished with a round nucleus, as in Plate II., Figs. 10 and 11, n n, and Stein has frequently noticed such young forms in localities where S. polymorphus, S. cæruleus, and S. Roesellii abounded. These forms may be the young of cœruleus, but it could not be ascertained from which of the species common in the locality they were derived. At a later period they were developed into a young chlorophyll Stentor, and it was not certain whether it belonged to polymorphus, or it might have been a young S. igneus. Stein observes that it would be a great mistake to infer identity of species from the fact of the young being indistinguishable, as this is the case in many creatures whose adult forms show them to be widely separated species.

Twice in January, and at the end of November, he met with green Stentors encysted, as shown in Plate I., Fig. 3, and in a locality in which S. polymorphus was abundant. Each time the cyst exhibited a peculiar structure. It was a broad egg-shape, sharply truncated at the small end, and provided with a broad circular mouth, closed with a well-fitting stopper, b, which protruded upwards in a half-round knob. The colourless and transparent cyst wall, a, was of considerable thickness, and plainly showed that it was formed out of thin superimposed layers. The stopper was composed of the same material as the cyst wall, but was somewhat softer, and not so plainly laminated. The enclosed animals completely filled its cell, and turned its hinder funnel-shaped end towards the stopper. The rounded front end lying at the bottom of the "Nucleolus " is not here intended to mean more than Stein's kerne, or kernel.