too PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. 
In V. aureus the colony is oftenest unisexual or dicecious, z.e. either 
male or female. But it may be moncecious or hermaphrodite, and is 
then generally protogynous, z.e. producing eggs first. 
Whether in a hermaphrodite or in a unisexual colony, the sex cells 
appear among the ordinary vegetative units ; the ova are distinguishable 
by their larger size, the ‘‘sperm mother cells” divide rapidly and form 
numerous (32-100 or more) slender spermatozoa, each with two cilia. 
In V. globator their bundles may break up within the parent colony ; 
or, as always occurs in V. aureus, they may escape intact, and swim 
about in the water. In any case, an ovum is fertilised by a spermato- 
zoon, and, after a period of encystation and rest, segments to form a 
new colony. Occasionally, however, this organism, so remarkable a 
condensation of reproductive possibilities, may produce ova which 
develop parthenogenetically. 
Here, then, we have an organism, on the border line between plant 
and animal life, just across the line which separates the unicellular from 
the multicellular, illustrating the beginning of that important distinc- 
tion between somatic or body cells and reproductzve cells, and occurring 
in asexual, hermaphrodite, and unisexual phases. Klein records no less 
than twenty-four different forms of V. aureus from the purely vegetative 
and asexual to the parthenogenetic, for there may be almost entirely 
male colonies, almost entirely female colonies, and other interesting 
transitional stages. Klein has also succeeded to some extent in showing 
that the occurrence of the various reproductive types depends on outside 
influences, 
Seventh Type of Protozoa—Mownocystis 
Monocystis, a type of Sporozoa in which the cell is zot 
divided into two parts by a partition. 
Description.—Two species (AZ agilis and MZ. magna) 
infest the male reproductive organs of the earthworm almost 
constantly. The full-grown adults are visible to the naked 
eye. They are usually flattened worm-like cells, but the 
shape alters considerably during the sluggish movements. 
There is a definite contractile rind, which is sometimes 
fibrillated, and a more fluid medullary substance, in which 
the large nucleus floats. In one species there is an anterior 
projection which resembles the cap of Gregarina, otherwise 
unrepresented in AZonocystis. As in Gregarina, and many 
_ other parasitic forms, a contractile vacuole is absent. 
Life history.—The young form of JZ. agitis is parasitic 
within one of the sperm mother cells of the earthworm. It 
grows, and becomes free from the cell as a trophozoite. In 
the free stage, two individuals may unite in the curious 
