28 THE MICROSCOPE AND ITS REVELATIONS. 



great rapidity; its movements, which are graceful and varied, being pro- 

 duced by the action of the flagella, which can not only impel it in any 

 direction, but can suddenly reverse its course or check it altogether. But 

 besides tbis free-swimming movement, a very curious ' springing ' action 

 is performed by this Monad when the decomposing organic matter of the 

 infusion is breaking up, the process of disintegration being apparently 

 assisted by it. The two posterior flagella anchor themselves and coil into 

 a spiral, and the body then darts forwards and upwards, until the anchored 

 flagella straighten out again, when the body falls forward to its horizon- 

 tal position, to be again drawn back by the spiral coiling of the anchored 

 flagella. This Monad multiplies by longitudinal fission; the first stage 

 of which is the splitting of the anterior flagellum into two (fig. 2, a, b), 

 and a movement of the nucleus (c) towards the centre. In the course of 

 from thirty to sixty seconds the fission extends down the neck fig. 3, ; 

 aline of division is also seen at the posterior end (c), and the nucleus 

 (b) shows an incipient cleavage. In a few seconds the cleavage-line 

 runs through the whole length of the body, the separation being widest 

 posteriorly (fig. 4, a); and in from one to four minutes the cleavage 

 becomes almost complete (fig. 5), the posterior part of the body, with the 

 two halves (a and b) of the original nucleus, being now quite disconnected, 

 though the anterior parts are still held together by a transverse band of 

 sarcode, as seen in fig. 6. This soon narrows and elongates, as shown in 

 fig. 7; and at last it gives way, setting the two bodies entirely free. The 

 whole process of fission, from first to last, is completed in from four to 

 seven minutes; and being repeated at intervals of a few minutes, this 

 mode of multiplication produces a rapid increase in the number of the 

 Monads. 



418. Such fission does not, however, continue indefinitely; for certain 

 individuals undergo a peculiar change, which shows itself first in the 

 absorption of the two lateral flagella and the great development of the 

 nucleus, and afterwards in the formation of a transverse granular band 

 across the middle of the body (fig. 8, a). One of these altered forms 

 swimming into a group in the ' springing ' state, within a few seconds 

 firmly attaches itself to one of them, which at once unachors itself, and 

 the two swim freely and vigorously about, as shown in fig. 9, generally 

 for from thirty-five to forty-five minutes. Gradually, however, a i fusion' 

 of the two bodies and of their respective nuclei takes place, the two trail- 

 ing flagella of the ' springing ' form being drawn-in (fig. 10); and in a 

 short time longer the two anterior flagella also disappear, and all trace of 

 the separate bodies is lost, the nuclei vanish, and the resultant is an 

 irregular amoeboid mass (fig. 11), which gradually acquires the smooth, 

 distended, and ' stiir condition represented in fig. 12. This a cyst filled 

 with reproductive particles of such extraordinary minuteness, that, when 

 emitted from the ends of the cyst (fig. 13) after the lapse of four or five 

 hours, they can only be distinguished under an amplification of 5,000 

 diameters, with perfect central illumination through an aperture in the 

 diaphragm of from l-80th to the l-100th of an inch in diameter. Yet 

 these particles, when continuously watched, are soon observed to enlarge 

 and to undergo elongation (figs. 15-17); and within two hours after their 

 emission from the sac, the anterior flagellum, and afterwards the two 

 lateral flagella (fig. 18) can be distinguished. Slight movements then 

 commence; the neck-like protrusion shows itself (fig. 19, a, b), and in 

 about half an hour more the regular swimming action begins. About 

 four hours after the escape of its germ from the sac, the Monad acquires 



