THE SPOROZOA 151 



sion in Coccidiida (Fig. 6, p. 20). Spore-formation is almost invariably 

 preceded by encystment, an exception being found in the Gymno- 

 sporea and Myxosporidiida. 



In general, it may be stated that the entire organism takes part in 

 the formation of archispores (or sporoblasts\ each archispore gives 

 rise to spores, and each spore to sporozoites, either .directly or indi- 

 rectly. Each spore, containing from one to many sporozoites, is coated 

 by either a single or a double membrane. When double, the inner 

 membrane is called the endospore, and the outer the epispore (Fig. 83, 

 F). The spores may be of similar or dissimilar size (inacrosporcs and 

 tnicrospores\ they may be ovoid, spherical, biconvex, cylindrical, 

 crystalline, discoid, etc., in form, and may be provided with diverse . 

 kinds of appendages, ridges, spines, etc., or with polar capsules con- 

 taining protrusible filaments (Myxosporidiida). In some cases there 

 is a special apparatus for the dissemination of the spores (sporodncts, 

 Fig. 85) ; in other cases, the spores are liberated by the simple 

 bursting of the outer envelope, or by the rupture of the walls through 

 swelling of a residual protoplasmic mass termed a pscudocyst. 



The process of spore-formation in the gregarine of an ascidian 

 Monocystis ascidice may be given as an example of a type common 

 to all Sporozoa, although in the several orders the details are vari- 

 ously modified. Two animals come together and form a common 

 cyst (Fig. 84, A). The nucleus of each divides by repeated mitoses 

 into a great number of daughter-nuclei, which soon arrange themselves 

 about the periphery (B, C) like the nuclei of a centrolecithal egg of 

 some Metazoa. A portion of the endoplasm is then budded off about 

 each of the daughter-nuclei, the buds thus formed becoming conju- 

 gating gametes. The bulk of the original cells is not used in this pro- 

 cess, a considerable portion which Labbe ('96) regards as a reserve 

 store of nutriment J remaining unused ( Theilungskorper, Cystenrest, 

 Reliquat de segmentation}. During this process the ectoplasm and 

 the membrane in each cell disappear, leaving the gametes and the cen- 

 tral residual masses within the cyst (D). The gametes now conjugate 

 two by two (E) to form the spores (sporocysts). Each of the spores, 

 which from their peculiar shape are known as pseudonavicelke t now in 

 its turn secretes two distinct membranes (epispore and endospore), and 

 within these the nucleus, with its surrounding plasm, divides into eight 

 parts which are disposed quite regularly in the spore (F\ As in the 

 formation of the archispores, a portion of the plasm is usually left 

 unused (Sporenrest, Restkb'rperchen, Reliquat de differentiation}. Each 

 of these parts is a sporozoite, which, after a developmental period, 

 reproduces an adult gregarine. When mature, the spores or pseudo- 

 navicellae are liberated by the bursting of the outer cyst-walls, brought 



1 See, however, Thelohan, '95. 



