MITOCHONDRIA IN AMOEBA 127 



secreted, or merely have secreted around them a watery vacuole, 

 the well-known food vacuole (Fig. 59, B). The food particle 

 commences to disintegrate as digestion proceeds, the mitochondria 

 enclosed by the vacuole with the food become smaller and less 

 densely staining (Fig. 59, D, E). Finally the mitochondria inside 

 disappear ; the food vacuole becomes very small, indicating the 

 passage of digested foodstuffs out into the cytoplasm (Fig. 59, F), 

 and the faecal remains are shot out. It is a matter for remark 

 that although many mitochondria become attached to the outer 

 surface of the food vacuole during its passage through the cell, 

 not one has been seen to pass through and enter the vacuole and 

 take part in the processes of digestion which are undoubtedly 

 going on inside. No mitochondria appear able to pierce the 

 vacuolar " membrane " or surface when once it is formed, so that 

 only those actually adhering to the food particle are included 

 within the vacuole. 



There is not much doubt that the mitochondria are largely 

 responsible in this case for the production of enzymes for the 

 process of digestion. It is probable also that they actually 

 give up their own substance for this purpose, for even if we 

 assume that they merely become unstainable rather than actually 

 disintegrate, it must be admitted that they never take any further 

 part in the activity of the cell, as they would be cast out with the 

 faecal remains. Before continuing with this particular line of 

 inquiry, some other work by Horning must be mentioned in connec- 

 tion with the form and structure of the mitochondria. 



He has traced the various stages of the mitochondria through 

 the life cycle of Opalina (59) and Monocystis (66). In the first case 

 {Opalina), he finds them as twisted filamentous structures under- 

 going multiple longitudinal fission in the asexual multiplicative 

 phase of the cell. Before encystment they undergo transverse 

 fission rej^eatedly to produce spherical bodies, in which condition 

 they apparently remain during encystment and in the gamete 

 stage. When the zygote is formed they commence to fuse together 

 and form larger bodies, which secondarily break up into elongate 

 filamentous particles again, for the asexual phase. 



In Monocystis the mitochondria are present throughout the 



