4. 5. 6. a. Its extreme irritability; it contracts on the B. The movements which occur in contraction; 7. Stain with iodine or magenta; the cuticle uncoloured -the rest stained; the nucleus especially becomes deeply coloured. Treat with acetic acid; the contents soon disappear (except perhaps some swallowed bodies)—the cuticle later or not at all. Note the following points in various specimens a. Multiplication by fission; a bell partially divided into two by a vertical fissure starting from the disc. B. Two complete bells on one of completion of the fission. stalk; the result The development of a basal circlet of cilia by one or both of these bells. [y. Free swimming unstalked bells (detached bells from B).1 [S. Conjugation; the attachment of a small free swimming bell to the side of a stalked one.] [e. Encystation; the body contracted into a ball and surrounded by a thickened structureless layer, the contractile vesicle being persistently dilated.] ཀྰ B. Other forms closely allied to Vorticella which may be met with, and which will do nearly as well for examination, are ;— a. Epistylis. Bell-shaped animals growing on a branched non-contractile stalk. b. Carchesium. A form very like Vorticella but borne on a branched contractile stalk. C. Cothurnia. An almost sessile form, provided with a cup or envelope into which the bell can be retracted. [The activity of the movements of the free Infusoria interferes with the complete examination of the living animal. It is well therefore to add a little osmic acid solution to the drop of water under examination. This kills such Infusoria as Paramecium, Nyctotherus and Balantidium instantly, without destroying the essential features of their organization.] X. THE FRESHWATER POLYPES (Hydra viridis and H. fusca). If a waterweed, such as duckweed, from a pond, is placed in a glass and allowed to remain undisturbed for a short time, minute gelatinous-looking bodies of a brownish or green colour may frequently be found attached to it, or to the sides of the glass. They have a length of from to of an inch, and are cylindrical or slightly conical in form. From the free end numerous delicate filaments, which are often much longer than the body, proceed and spread out with a more or less downward curve, in the water. If touched, these. threads, which are the tentacles, rapidly shorten and together with the body shrink into a rounded mass. After a while, the contracted body and the tentacles elongate and resume their previous form. These are Polypes, the brown ones belonging to the species termed Hydra fusca, the green to that called H. viridis. The polypes usually remain attached to one spot for a long time, but they are capable of crawling about by a motion similar to that of the looping caterpillar; and, sometimes, they detach themselves and float passively in the water.. When any small animal, such as a water-flea, swimming through the water comes in contact with the tentacles, it is grasped, and conveyed by their contraction to the ལ B. Other forms closely allied to Vorticella which may be met with, and which will do nearly as well for examination, are ; a. Epistylis. Bell-shaped animals growing on a branched non-contractile stalk. b. Carchesium. A form very like Vorticella but borne on a branched contractile stalk. C. Cothurnia. An almost sessile form, provided with a cup or envelope into which the bell can be retracted. [The activity of the movements of the free Infusoria interferes with the complete examination of the living animal. It is well therefore to add a little osmic acid solution to the drop of water under examination. This kills such Infusoria as Paramecium, Nyctotherus and Balantidium instantly, without destroying the essential features of their organization.] |