9 8 
F. Cavers. 
by brood formation which is often of alternating types. The two 
most characteristic features of the Sporozoa are obviously correlated 
with their parasitic mode of life—they absorb fluid food osmotically 
and therefore lack organs for ingestion of solid food and they reproduce 
by the formation of minute germs, usually very numerous and often 
enclosed in firm protective envelopes, each with its contents con¬ 
stituting a spore. In most cases there is a second method of 
reproduction for increasing the number of the parasites in the 
individual host—this is distinguished as multiplicative or self- 
infective or endogenous reproduction from the propagative or cross- 
infective or exogenous method (by means of resistant spores) which 
serves for infection of fresh hosts; and in most cases also sexual 
conjugation occurs at some period of the life cycle. The Sporozoa 
fall into two natural divisions, the Ectospora (Gregarinida, Coccidia, 
Haemosporidia) in which the spore mother cells (sporoblasts) are 
formed at the periphery of the parent individual, and the Endospora 
(Myxosporidia, Actinomyxidia, Sarcosporidia, Haplosporidia, 
Exosporidia, Serosporidia) in which the spore mother cells arise in 
the interior of the body of the parent; that is, in the Ectospora 
sporulation is exogenous, in the Endospora it is endogenous. A 
further very general though not universal distinction between the two 
divisions is that in the Endospora sporulation goes on coincidently 
with vegetative (growth and trophic) life, while in the Ectospora it 
does not begin until the close of the vegetative or trophic period, 
i.e., until growth has ceased; on this account Schaudinn suggested 
for these divisions the terms Neosporidia and Telosporidia respec¬ 
tively. Moreover, a general distinction lies in the fact that the 
body in the Endospora is multinucleate but in the Ectospora uni¬ 
nucleate during the trophic period. 
The Infusoria as defined by the dual nature of the nuclear 
apparatus—the meganucleus usually dividing by constriction and 
disappearing during conjugation, the micronucleus (sometimes 
multiple) dividing by mitosis and entering into conjugation and 
giving rise to the nuclei both large and small of the succeeding 
generation—fall into two divisions. The Ciliata, representing the 
highest type of Protozoa, have cilia or organs derived from cilia 
throughout life, are provided with a single permanent mouth 
(except in the parasitic Opalinopsidae) flush with the body or at the 
base of an oral groove, and take in food by active swallowing or by 
ciliary action ; while the Suctoria are rarely ciliated except in the 
young state and take in food by suction through protrusible hollow 
tentacles. 
III.— The Colourless Flagellata. 
From a general survey of the characters of the diversified 
forms of Protista classed by zoologists in the Protozoa it is fairly 
obvious that this heterogeneous group may for our present purpose 
be roughly divided into two main sections, one including a large 
proportion of generalised and relatively primitive forms, while the 
other comprises more complex and specialised forms. The gener¬ 
alised groups are the Flagellata and Sarcodina, among which there 
are forms which lead to the primitive Algae, to the primitive Fungi 
and to the two specialised Protozoan groups—the Sporozoa and 
the Infusoria. 
