28 
those characteristics which decide its place in the scale of beings in corres- 
pondence with its life-history. Cienkowski's definition of a Monad is based 
on the idea of a unicellular individual, whose spores pass by metamorphosis 
into Amseboid plasms, and like the typical Amaebas take in foreign bodies 
into their substance as aliment. Other characteristics of the cell condi- 
tions, during its process of encystation, are included in Cienkowski's 
description of Monad. The basis of Cienkowski's definition is more 
morphological than physiological. 
Figs. 14-18 shew P. volvocis, a parasite of the V. globator. Like the 
former, its Zoospore (but much larger) has a nucleus and two cilise. The 
amoeboid phase is easily reached without losing its cilise. The creature 
creeps over the surface of volvax, and finally bores its way inside 
it, devouring in a few days all the colony of young volvoces, and then 
abandoning this for a new prey. On changing its state, it forms a cyst 
which is outwardly circumscribed by another membrane or veil of irregular 
dimensions, which corresponds to the outline of its former Amoeba state, 
whilst within the cyst, which has a double contour, lies the rounded cell 
in which reproduction goes on. According to this description, the P. 
volvocis is not a Moner as defined by Hseckel. 
Cienkowski describes also as a Monad a new species, to which he gives 
the name Colpodella pugnax, which I mention here on account of its amusing 
history. Figs. 19-30 refer to it. In this creature the Amoeboid phase is 
missing. Its Zoospore appears first in the shape of a sickle or lunette with 
pointed ends and is quite colourless. It has a nucleus, a vacuole, and one 
cilium at its anterior extremity. Its motion is tremulous as it swims, 
occasionally varied by vigorous -sweeps of its posterior extremity. It is 
found in company with " Chlamydomonas pulvisculus, " and falls foul of 
its neighbour, fastening upon it with its nonciliated end. In a few seconds 
the green contents of the primordial sac of its prey may be seen very slowly 
entering into the Zoospore's body, and the pointed end which serves as 
mouth widens. The attacking Zoospores at length suck out their victim, 
and quit it for another, till they fill out in dimensions and resemble the 
Colpoda in shape, with a curved extremity, which he bears forward in his 
agitated movements. 
The Colpodella Zoospore must have therefore the power to pierce or dis- 
solve the membranous covering of the Chlamydomonad. For if, after the 
first attack, the Zoospore leaves its prey, green matter flows out of the 
small opening made just where the Zoospore fastened itself. The vegetable 
Zoospore (Chytridia) has however the same power of piercing or dis- 
