758 MICROSCOPIC FORMS OF ANIMAL LIFE 



was only after much effort that we at last, by keeping the finest of our 

 lenses near the mouth of the empty sac, were able to discover, where 

 before nothing was visible, the appearance of minute specks, which 

 became larger and larger, growing as seen in 14, 15, 16, 17, until 

 the adult size was reached, as at is, and by the act of multipartitioii 

 on the part of one of these, watched from its first disclosure by the 

 microscope, we were able to re-enter the cycle of its life-history. 



The third form, which we may here consider fully, so as to present 

 a good group of histories typical in their presentation of the morpho- 

 logy of the whole of the monad-saprophytes as we at present know 

 them, is given in E and F, Plate XV. 



The monad has been named by S. Kent Dallingeria Drysdall. 

 The form more recently and completely studied by Mr. Dallinger 

 with all the advantages derived from trained experience, and under 

 objectives of the highest quality and greatest magnifying power is 

 seen in its normal shape in fig. l,,is a long oval, slightly constricted 

 in the middle, and having a kind of pointed neck (), from which 

 proceeds a nagellum about half as long again as the body. From 

 the shoulder-like projections behind this (b, c,) arise two other long 

 and fine flagella, which are directed backwards. The sarcode-body 

 is clear, and apparently structureless, with minute vacuoles dis- 

 tributed through it ; and in its hinder part a nucleus (d) is dis- 

 tinguishable. The extreme length of the body is seldom more than 

 the oVoth of an inch, and is often the ^^th. This monad swims 

 with great rapidity, its movements, which are graceful and varied, 

 being produced by the action of the fiagella, which can not only 

 impel it in any direction, but can suddenly reverse its course or check 

 it altogether. But besides this free-swimming movement, a very 

 curious ' springing ' action is performed by this monad when the de- 

 composing 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 horizontal 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. - J, a, 5), 

 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, a) ; a line 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 separa- 

 tion 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, which 

 continues to rapidly elongate, as in fig. 7, and becomes the length of 

 two side flagella, as in fig. 8. The forms then approach and rapidly 

 recede from each other, snapping the cord, as in figs. 9 and 10. In 

 this way two forms exist instead of one ; and each of these almost im- 



