238 D. D. CUNNINGHAM. 
nourished at the expense of an active amcboid organism, it 
becomes adherent to it by its posterior extremity. The Ameba 
at first continues to progress freely, but soon ceases to do so, 
assumes a spherical and motionless condition, and is dragged 
passively about by the energetic flagellary movements of the 
zoospore. Gradually a diminution in its bulk becomes manifest, 
the body of the zoospore at the same time becoming distinctly 
plumper and more refractive, and as the process continues the 
whole, or almost the whole, of the Amceba disappears, and its 
plunderer swims off to seek a new victim. Sometimes several 
zoospores unite in plundering one Ameeba, which is jerked irregu- 
larly about by their opposed movements. In the case where 
red blood-corpuscles are the source of nutriment, as is fre- 
quently the case in choleraic evacuations, the progress of the 
process may be followed readily by the colouring of the zoospore- 
body by the absorbed hemoglobin. In some cases portions of 
corpuscles, too, seem to be absorbed ex masse, though it is 
difficult to be quite certain on this point, due to appearances 
arising from surface adhesion to the transparent bodies of the 
zoospores. 
Owing to the constant movements presented by the parasites 
when in full activity, it is difficult to come to any definite con- 
clusion regarding the frequency with which they possesss a 
differentiated nucleus or contractile vesicle. That they do do soin 
some cases there can be no doubt, but in many the most careful 
and prolonged examinations fail to reveal the presence of either 
structure. That the presence or absence of a distinct contractile 
vesicle is not a matter of essential specific importance, is the 
conclusion which Hertwig and Lesser seem to arrive at as the 
result of their study of the Rhizopoda,! and the phenomena 
presented by the organisms at present under consideration cer- 
- tainly corroborate thisconclusion. The presence of a contractile 
vesicle appears to be an inconstant character, determined, in 
some cases at all events, by conditions of the nutritive medium. 
With regard tothe constancy of a nucleus as a specific cha- 
racter, it is necessary to speak with some reserve, as the presence 
of such a structure may readily escape observation in such 
minute organisms as the excretal zoospores. This is more 
especially likely to occur where a distinct nucleolus is not 
present and where the nucleus is merely represented by a clear 
vacuolar area in the body-mass. That these conditions may 
replace one another in one and the same organism is, as we shall 
see hereafter, unquestionable, bodies which at one period merely 
show a clearer nuclear area subsequently showing a conspicuous 
1 “Ueber Rhizopoden und denselben nahestehende Organismen,” ‘ Ar- 
chiv fir mikr, Anat.,’ Bd. X. Suppl. 
