PROTOZOA 33 



The term spore is applied to various phases of the life history in a 

 way which is liable to cause confusion, {a) Strictly speaking, perhaps, 

 it should be applied only to the products of repeated or multiple 

 fission of the zygote (sporont). {b) Most often, however, it is used to 

 denote the products of any repeated or multiple fission, (c) In a 

 few cases (e.g. the " ciliospores " of the Suctoria) it is applied also 

 to products of budding. A cyst in which several spores are enclosed 

 is a sporocyst. Individual spores may be enclosed in spore cases^ when 

 they are chlamydospores (as those of the Mycetozoa, Fig. 73 A), or 

 naked, when they are gymnospores . The latter may be amoeboid 

 (amoebulae or pseudopodiospores, e.g Amoeba, Polystomella, Fig. 66 C), 

 flagellate {flagellulae or fiagelltspores, e.g. Polystomella, Fig. 66 B, 

 Chlamydomonas), or ciliate {ciliospores, e.g. the Suctoria, Fig. 86 H). 

 Spores maybe gametes (e.g. the Mycetozoa, Chlamydomonas), or serve 

 for the distribution of the species, when, if they are motile, they are 

 known as "swarm spores". The sporoblasts of many telosporidia 

 (e.g. Plasmodium, Fig. 75, 16-18) are spore-like bodies which are 

 not set free, but give rise under cover to another generation of spores. 

 The so-called spores of such sporozoa as Monocystis (Fig. 78 G, H) 

 are really minute sporocysts, enclosing several spores ("falciform 

 young"). 



The life history of the individual protozoon usually exhibits little 

 change save increase in size. Sporozoites and other spores, however, 

 may differ considerably from the adults into which they grow. This 

 diff"erence reaches its height in the ciliospores of the Suctoria. 



The life of a protozoon, of which those actions which we call its 

 behaviour are the conspicuous part, is, like the life of higher organ- 

 isms, the sum of innumerable activities — mechanical, chemical, etc. — 

 of which some, such as the direction of locomotion to or from the light, 

 are immediately due to external circumstances {stimuli), while others, 

 such as the beating of cilia which continues even when the organism 

 is encysted, are not. Both kinds of activity are so ordered that in 

 normal circumstances they conduce to the welfare of the organism. 

 The reactions to stimuli are superficially analogous to the reflexes of 

 the Metazoa. Study of them has chiefly been directed to those which 

 result in locomotion. Such reflexes are of two kinds, topotaxis and 

 phobotaxis. In topotaxis the organism orientates itself in relation to 

 the stimulus, and moves either towards or away from it. This is the 

 less common mode of reaction in protozoa, but it appears to be per- 

 formed by some in the neighbourhood of food, by gametes in their 

 union, and by certain green flagellates {Volvox, sometimes Euglena, 

 etc.) in approaching the light. 



In phobotaxis, which has been studied in many protozoa of various 

 groups, the only circumstances which act as stimuli are those which 



