30 THE MICROSCOPE AND ITS REVELATIONS. 



becoming amoeboid and less active; and when two of these came into con- 

 tact, they underwent a complete fusion, the product of which was a 

 globular cyst, with a very definite investment, filled with reproductive 

 germs. The ( springing Monad' of the same observers (Heteromita ros- 

 trata, Kent) is of a long ovate form, with an average length of about 

 l-3000th of an inch. From its narrower extremity a sort of beak arises, 

 from which proceeds a fine flagellum about half as long again as the body; 

 and at a little distance behind this, another and longer flagellum arises, 

 with which the Monad anchors itself to the covering-glass, constantly 

 springing backwards and forwards by its recurrent coil and uncoil. A 

 nucleus shows itself near the rounded posterior end of the body. This 

 Monad multiplies by longitudinal fission, commencing at the beaked end, 

 and completed in six or seven minutes; and the process may be repeated 

 continuously for many days. Among enormous numbers, there are a 

 few distinguishable from the others by a slight excess of size, and by the 

 power to swim freely; these become ' still ' for a time amoeboid then 

 round; a small cone of sarcode pushes out, dividing and increasing into 

 another pair of flagella; the disk splits, each part becomes possessed of a 

 nuclear body, and two well-formed free-swimming Monads are set free. 

 These conjugate with individuals of the ordinary form which have just 

 undergone fission, the nuclei of the two approximating to each other; a 

 complete fusion of sarcode and nuclei takes place; the body, at first 

 motile, comes to rest, assumes a triangular form, and loses its flagella; 

 it then becomes clear and distended, and emits its contained reproductive 

 granules at the angles. The ' hooked Monad' (Heteromita uncinata, 

 Kent) is another bi-flagellate form, usually ovate with one end pointed, 

 and from l-3000th to l-4000th of an inch in length; being distinguished 

 from the preceding by the peculiar character of its flagella, of whicn the 

 one that projects forward is not more than half the length of the body, 

 and is permanently hooked, while the other, whose length is aoout twice 

 that of the body, is directed backwards, flowing in graceful curves. Its 

 motion consists of a succession of springs or jerks rapidly following each 

 other, which seems produced by the action of the hooked flagellum. 

 Multiplication takes place by transverse fission, and continues uninter- 

 ruptedly for several days. A difference then becomes perceptible between 

 larger and smaller individuals; the former being further distinguished by 

 the presence of what seems to be a contractile vesicle in the anterior part 

 of the body. Conjugation occurs between one of the larger and one of 

 the smaller forms, the latter being, as it were, absorbed into the body of 

 the larger; and the resulting product is a spherical cyst, which soon begins 

 to exhibit a cleavage-process in its interior. This continues until the whole 

 of its sarcodic substance is subdivided into minute oval particles, which 

 are set free by the rupture of the cyst, and of which each is usually fur- 

 nished with a single flagellum, by whose lashing movement it swims 

 freely. These germs speedily attain the size and form of the parent, and 

 then begin to multiply by transverse fission thus completing the ' gene- 

 tic ' cycle. 



421. The ' calycine Monad ' of the same observers (Tetramitus rostra- 

 tus, Perty), has a length of from l-900th to l-1000th of an inch, and a 

 compressed body tapering backwards to a point. Its four flagella (which 

 constitute its generic distinction) arise nearly together from the flattened 

 front of the body; and its swimming movement is a graceful gliding. 

 Xear the base of the flagella is a pair of contractile vesicles; and further 

 behind is a large nucleus. Multiplication takes place by longitudinal 



