SAPROPHYTIC LIFE-HISTORIES 763 



Xot less remarkable is this in the conjugation of the same form. 

 With the old lenses \ve could only discover that the end of a 

 series of fissions had been reached by the change which came over 

 the entire body of the terminal form seen in fig. 11, E. Plate XV. 

 But now. before the amoeboid state preceding the assumption of 

 the condition shown in fig. 11 takes place, it can be seen that the 

 nucleus undergoes remarkable change, for it passes from a highh 

 refractive plexus-like condition into a large milky structureless stair, 

 and in this condition blends with one of the ordinary forms whose 

 nucleus is of the ordinary type. The first result of fusion is seen in 

 fiy. 4. A, Plate XVI. showing only the greatly magnified blended 

 nuclei, and where the blending between them is seen to be nearly 

 complete at a. and a nucleus or nucleolus is manifest ; while 

 when the blending is more perfect there is a diffusion of this 

 central or iiucleolar body through the substance of the whole, as in 

 fig. 5, A. 



In B, Plate XVI. the nucleus only, separate from the body of 

 the organism known as Tctrn mitus i-ostr(iti>x. is shown as we can 

 reveal it with recent (-Serman and English apochromatic objectives. 

 This entire organism is relatively large, and its nucleus will average 

 in long diameter the iTnrooth <>f an inch. 



Hence it affords a still better means of study. Xow this 

 organism divides by fission for a very considerable time, hut at length 

 many forms become anueboid acting precisely as an a nice ha. but 

 retaining traces of their primal form. In this state two of them 

 blend, and as a result a sac of spore is formed from which a new 

 generation arises. 



\\ e could with the old objectives determine nothing more than 

 the fact that the anm>boid form had supervened ; but now it is easy 

 to show that the nucleus in the body of a form not yet amoeboid is 

 undergoing change upon which the aimrboid slate is certain to 

 supervene. 



This is even more striking in the growth of the germ. It attains 

 a certain size in growth, and then there is an arrest of all enlarge- 

 ment. This we had long ol (served in the earlier observations. But 

 now with apochromatic object-glasses it has been demonstrated that 

 this arrest of outward growth is only the signal for an internal de- 

 velopment. Fig. I , B, Plate XVI, shows the condition of the nucleus 

 when there is an apparent pause in its growth. Fig. -2 shows the 

 same nucleus after about forty minutes of external inaction, a plexus- 

 like formation having filled its substance. 



The nucleus remains thus in the mature body of the monad 

 until fission is to he inaugurated, when the change seen in fig. :>, 

 followed by the changes and deeper division seen in figs. 4. 5, 6, 7, 

 and s, ensue, and after the state of the nucleus seen in fig. 4 has 

 been reached, the division of the entire body begins. 



It thus appears that a form of Jcaryokinesis takes place in the 

 nucleus of even such lowly forms as these, and that it is the nucleus 

 that is the seat of their intensest vitality. 



A large series of more complex forms of flagellate Infusoria 

 has been brought to our knowledge by the researches of the late 



