A.

I.

2.

LABORATORY WORK.

MORPHOLOGY.

a. Resting or stationary Protococcus.

Spread out in water some mud from a gutter or similar locality, and put on a cover-glass. Look for the red or green protococcus cells with a low power. Having found some, put on a high power and make out the following points.

Size; (measure)-very variable.

Form; more or less spheroidal, with individual

variations.

Structure; sac-protoplasm-sometimes a vacuolesometimes apparently a nucleus. (Compare Torula, I. A. 2. b.)

Colour; generally green-sometimes red-sometimes
half and half-sometimes centre red, periphery
green-the colouring matter always in the pro-
toplasm only-most frequently diffused, but
sometimes in distinct granules, or oily looking
drops.

Note especially the following forms of cell—
a. The primitive or normal form.

Roundish cells, with a cellulose sac, and unseg-
mented granular contents. Draw several carefully
to scale. Apply the methods of mechanical and
chemical analysis detailed for Torula. (I. A. 3. 4.
5. 6.) Note that iodine in some cells produces a
blue coloration by its action on the red matter
present. Treat a specimen with strong iodine
solution and then with sulphuric acid (75 per
cent.): the sac will become stained blue.

b.

a.

Cells multiplying by fission:

Simple fission. The cell elongates, and the protoplasm divides into two across its longer axis, and then a partition is formed subdividing the sac; the halves either separate at once, and each rounds itself off and becomes an independent cell; or one or both halves again divide, in a similar way, before they separate, and so three or four new cells are produced.

B. Cells multiplying by budding, like Torula; rare. b. Motile stage.

Mount a drop of water containing motile Protococcus, and examine with a high power. Note. the actively locomotive green bodies, of which two varieties can be distinguished.

Cells like the stationary ones in size, and apparently directly formed from them. Each possesses a structureless colourless sac, surrounding the coloured protoplasm, but the latter has shrunk away from the sac at most points.

Note in various specimens-The two cilia prolonged from the protoplasm through apertures in the sac; their motionless part within the sac; their vibratile portion outside it. The colourless thin external layer of the protoplasm collected into a little heap at the point from whence the cilia arise. The delicate colourless processes radiating from the outer protoplasmic layer to the interior of the sac. The colour-usually green, but frequently one bright red spot is present.

B. Cells much like the above if the cellulose sac were removed, and the radiating processes extending to it from the protoplasm withdrawn.

b. Try to find specimens in which the movements are becoming sluggish, and see the cilia in motion.

C.

Stain with iodine: this kills the cells, and stops their movements; and frequently renders the cilia very distinct.

[B. PHYSIOLOGY.

Get some water that is quite green from containing a large quantity of Protococcus; introduce some of it into two tubes filled with and inverted over mercury, and pass a small quantity of carbonic anhydride into each: keep one tube in the dark and place the other in bright sunlight for some hours. Then measure the gas in each tube and afterwards introduce a fragment of caustic potash into each; the gas from the specimen kept in the dark will be more or less completely absorbed (= carbonic anhydride), that from the other will not be absorbed by the potash alone, but will be absorbed on the further introduction of a few drops of solution of pyrogallic acid (=oxygen). Protococcus, therefore, in the sunlight, takes up carbonic anhydride and evolves oxygen. A comparative experiment may be made with a third tube containing water but no Protococcus.]

III.

THE PROTEUS ANIMALCULE (Amaba).
COLOURLESS BLOOD CORPUSCLES.

Amabæ are minute organisms of very variable size which occur in stagnant water, in mud, and even in damp earth, and are frequently to be obtained by infusing any animal matter in water and allowing it to evaporate while exposed to direct sunlight.

An Amaba has the appearance of a particle of jelly, which is often more or less granular and fluid in its central parts, but usually becomes clear and transparent, and of a firmer consistency, towards its periphery. Sometimes Amæbæ are found having a spherical form and encased in a structureless sac, and in this encysted state they exhibit no movements. More commonly, they present incessant and frequently rapid changes of form, whence the name of "Proteus Animalcule" given to them by the older observers; and these changes of form are usually accompanied by a shifting of position, the Amaba creeping about with considerable activity, though with no constancy of direction.

The changes of form, and the movements, are effected by the thrusting out of lobe-like prolongations of the peripheral part of the body, which are termed pseudopodia, sometimes from one region and sometimes from another. Occasionally, a particular region of the body is constantly free from pseudopodia, and therefore forms its hindmost part when

it moves. Each pseudopodium is evidently, at first, an extension of the denser clear substance (ectosarc) only; but as it enlarges, the central, granular, more fluid substance flows into its interior, often with a sudden rush.

In some Amaba a clear space makes its appearance, at intervals, in a particular region of the ectosarc, and then disappears by the rapid approach of its walls. After a while, a small clear speck appears at the same spot and slowly dilates until it attains its full size, when it again rapidly disappears as before. Sometimes two or three small clear spots arise close together, and run into one another to form the single large cavity. The structure thus described is termed the contractile vesicle or vacuole, and its rhythmical systole and diastole often succeed one another with great regularity. Nothing is certainly known respecting its function, nor even whether it does or does not communicate with the exterior, and thus pump water into and out of the body of the Amaba, though there is some reason to think that this may be the case.

Very frequently one part of the Amaba exhibits a rounded or oval body, which is termed the nucleus. This structure sometimes has a distinctly vesicular character, and contains a rounded granule called the nucleolus.

The gelatinous body of the Amaba is not bounded by anything that can be properly termed a membrane; all that can be said is, that its external or limitary layer is of a somewhat different constitution from the rest, so that it acquires a certain appearance of distinctness when it is acted upon by such reagents as acetic acid, or when the animal is killed by raising the temperature to 45° C. Physically, the ectosarc might be compared to the wall of a soap-bubble, which, though fluid, has a certain viscosity, which not only enables its particles to hold together and