LIFE HISTORY OF BODO 87 



which occurs in long-standing infusions of cod's head. It differs 

 from Copromonas chiefly in the possession of two flagella and in 

 the absence of a cell mouth, all its food being taken in in a state of 

 solution by diffusion through the thin cell membrane. The two 

 flagella both spring from the beak-like anterior extremity. One 

 (A, a.f.) extends forwards and by its movements enables the 

 organism to swim actively about, the other (A, t.f.) hangs down 

 and is trailed behind during active locomotion. The monad 

 anchors itself by the trailing flagellum and then, by coiling and 

 uncoiling the latter, executes characteristic springing movements. 

 Asexual reproduction (i.e., reproduction without any sexual 

 process) is effected by simple fission, which may be either 

 longitudinal (B, C) or transverse (D F). 



There are no structurally differentiated gametes or sexual 

 cells, but conjugation (G J) is effected between two apparently 

 similar individuals which are indistinguishable from the ordinary 

 form. It is noteworthy, however, that one of the two gametes at the 

 time of union is anchored, while the other swims actively up to it, 

 and thus we get a slight indication of physiological differentiation 

 into active and passive, or male and female. The male gamete 

 also arises by a somewhat peculiar method of fission. Conjugation 

 of the two gametes produces a zygote which has somewhat the 

 shape of a triangular sac (K). The flagella disappear and in the 

 interior of the sac cell-division goes on with great rapidity, giving 

 rise to an immense number of very minute spores, which ultimately 

 escape from the corners of the sac in the form of very fine dust 

 (L, sp.). Each spore no doubt is a minute nucleated cell, but it is 

 so small that the nucleus cannot at first be made out. It grows 

 by absorbing liquid food from the infusion in which it lives, and 

 as it grows the nucleus becomes apparent, flagella are put forth, 

 and the adult form is gradually attained (M). We have here a 

 striking illustration of the fact that the most obvious result of 

 conjugation is an increase of the power of cell- division. 



As a case of complete morphological as well as physiological 

 differentiation between male and female gametes in a unicellular 

 organism we may take that of Coccidium schubergi, which occurs 

 as a parasite in the intestine of a centipede (Lithobius forficatus). 

 The life history of this remarkable protozoon is very com- 

 plicated and it is not necessary for our purposes to describe it 

 in detail. The adult organisms occur in the form of spherical 

 nucleated cells, each actually inside one of the epithelial cells 



