It is constant in position except in the amoeboid condition, and is frequently placed at the base of the flagellum or laterally; it is superficial except in some Euglenoids where it debouches into a reservoir opening in its turn into the oesophagus.

1 The old stems of Anthophysa become brown; the granules visible in the substance of the young stem appear to be of an excretory nature. In an animal fed with indigo or carmine the particles of this pigment are soon excreted, and stored up in the newly formed portion of the stem.

2 Kent states (Manual of the Infusoria, p. 380) that he observed not only accumulations of particles of carmine in the body of Euglena viridis when that animal was kept in water, containing in suspension finely pulverized carmine, but also the entrance of particles at the anterior extremity of the oesophagus.

3 The ingestion of solid food by a coloured form Chromulina (Chrysomonas) flavicans is beyond doubt, and it possibly occurs in other instances. Some colourless forms (septic monads) have been observed to take in solid particles in quantity when in an amoeboid state. Bodo caudatus is able to pierce the cuticle of Chlamydomonas, and even of Infusoria, and to suck out the contents by means of its mouth.

The nucleus has not been observed in some of the smallest forms. It is typically vesicular, and in Euglenoids often reticulate with or without a nucleolus. Trepomonas has two nuclei, other Flagellata only one. A diffuse colouration of the protoplasm never occurs. Chromatophores, always superficial in position, are common in certain groups, e. g. Isomas-tigoda. They are firm, soft, of definite shape, and consist of a colourless basis infiltrated with green chlorophyl or brown diatomin, or a mixture of both substances in variable proportion; hence a corresponding variation in their tint. They multiply by fission. They are numerous, small, round, or oval in Euglenoids, two in number, large and plate-like in Dinobryon, etc.; single and enveloping the whole surface in Chlamydomonas^ Gonium, and probably in other Chlamydomanadina and Volvocina. Allied forms may be coloured or colourless, e.g. Chlamydomonas and Polytoma, Crypto-monas and Chilomonas; and colourless species may occur in coloured genera, e. g.

Euglena 1 Clear bodies, one or more, known as pyrenoids or amylum-bodies, are found in connection with the chromatophores of some Euglenoids, of Chlamydomonads and Volvocina. They multiply by fission and consist of a core, the pyrenoid, a clear substance which stains readily, coated in nearly all instances with starch or amylum, rarely with paramylum. Starch granules have been observed scattered in the protoplasm of Cryptomonas as well as in some colourless saprophytic forms when well nourished, e. g. Chilomonas. Paramylum, a substance of the same centesimal composition as starch, but not stained by iodine, occurs as laminated grains of varying size, oval, rod- or ring-like in shape, in the protoplasm of Euglenoids2. When the green-coloured organism passes into a resting phase, and rarely while it remains motile, its colour changes to red owing to the formation of haematochrome dissolved in droplets of fat. The formation begins centrally, and spreads to the periphery, disappearing in the reverse direction. It masks the chromatophores when they do not, as is sometimes the case, entirely vanish.

Special red-specks, the eye specks or stigmata, of a rounded or rod-like shape, simple, or when large composite, are present to the number of one or more in most coloured and in some colourless forms. They may be placed near the base of the flagellum, the middle of the body (Volvocina, some Chlamydomonads), or even at its hinder end (other Chlamydomonads). A lens-like structure is said to co-exist with the stigma in the Euglenoid Phacus, and a colourless strongly refractile body in the position of a stigma in some colourless forms, e. g. Monas. The function of the stigmata is doubtful, but they are said to disappear in darkness. Forms devoid of them are said to react to light in the same way as those which possess them. Trichocysts similar to those of Infusoria, are lodged at the anterior end of the freshwater Euglenoid Gonyostomum s. Merotricha semen; their presence elsewhere is doubtful.

1Polytoma and Chilomonas live in putrifying solutions, and are saprophytic, as are also colourless Euglenae. Chlorogonium and Carteria (Chlamydomonads) are said to become colourless under conditions in which they may be saprophytic.

2For the characters of paramylum, see Biitschli, Protozoa, Bronn's Thierreich, i. pp. 727-30. Amyloplasts, or starch-builders, are said to be present in Chilomonas (Fisch, Z. W. Z. xlii. 1885, p. 82). For these starch-builders, see Sachs' Lectures on Physiology of Plants, transl. by Ward, 1887, p. 316, and Schimper, Q. J. M. xxi. 1881.

Reproduction takes place by fission in the free or encysted state, the latter being frequently preceded by conjugation. Fission in the free state may be binary, and it may be continued without an interval for the growth of the -progeny. It is sometimes transverse, but as a rule longitudinal. It occurs while the organism is in the flagellate motile condition, rarely when the flagella have been cast off, the organism remaining motile or becoming motionless as in some Euglenina^ or still more rarely when it is amoeboid as in Ciliophrys, the two products in this case being flagellate. Details vary, but fission of the organism itself occurs only after the principal organs have been already doubled by division, or by new formation as is the case with the contractile vacuole, and sometimes with the flagella even in longitudinal fission. Repeated fission takes place in some Chlamydomads under the protection of the cuticle while the parent organism is motile, and sometimes results in the formation of numerous small individuals or microgonidia. The products are set free by rupture of the cuticle which may be gelatinised previously. Encystation previous to fission occurs in some species of Etiglena, etc.