1921] NATURAL SCIENCES OF PHILADELPHIA. 125 



gellum (either by a simple cutting, or perhaps, as it sometimes 

 seemed to be, by separation of two flagella, which existed before 

 but were glued together); at the same moment, the plasmatic tube 

 divides and soon retracts on each of the new individuals. As soon 

 as the separation is achieved, the upper individual oscillates on the 

 rim of the shell, turns slowly down, and its flagellum is then seen 

 pointing forwards. The little organism contracts somewhat, and 

 remains quiet for some time, then suddenly darts forward, carrying 

 in front of it a very long flagellum, longer, it seems, that it will be 

 afterwards (Plate VI, fig. 22). It swims very rapidly, describing 

 large circles, then suddenly stops, rests for a time, starts and swims 

 again, rests, and so on for probably a long time, but I could not 

 determine the period. The length of the animalcule is 7[i. One 

 sees easily the anteriorly placed nucleus, and behind a large con- 

 tractile vesicle, sometimes with an accessory one; a short proto- 

 plasmic collar is also present. The entire process, from the moment 

 when both individuals are distinctly separated but yet quite near 

 . each other, to the darting away of the little flagellated animalcule, 

 has lasted but six or seven minutes. As for the lower individual, 

 which remained in the cell, it expanded in a few minutes also. 



But things are often quite different: the young animalcule, which 

 has just disengaged from the cell, instead of darting forward, re- 

 mains quiet for a time, as if hesitating, then, with a few very weak 

 downward beatings of the flagellum, slips along the exterior wall of 

 the shell it has just left, and soon settles quite near, lying along the 

 mucilaginous covering of the Zygnema (Plate VI, fig. 24, a). How- 

 ever, it very soon stands up straight on the jelly (Plate VI, fig. 24, 6), 

 and ten minutes after the first contact with the substratum it is 

 already seen to have produced a very short root (c), which soon 

 will reach the cellulose wall {d, e, /). But during that time also, 

 the first rudiments of the new envelope are deposited, a thin film 

 around the body, along which the animalcule soon rises, leaving 

 the empty posterior end of the capsule behind. In fig. 23, which 

 is an enlargement of/ in fig. 24, the body is seen to swell out later- 

 ally, so as to press everywhere on the anterior part of the cell and 

 enlarge it, somewhat like a potter wdio moulds his clay, but in- 

 stead of a finger, the whole body is here employed. A little later 

 (Plate VI, fig. 24, g), the body has retracted a little, the widened 

 borders of the capsule are free, and are even too much expanded 

 but will soon contract a little. The animalcule, however, moves 

 more and more upward, and finally shapes up the aperture of the 



