SPOROZOA 99 



syngaiuy or siiore-foriiiaticui ; soiuetiines IVoiu two to five may 

 be aggregated into a cliaiu or " syzygy." The number of cases 

 in which a syngamic process between two cells has been observed 

 is constantly being increased. In Stylorliynchus (Fig. 33) the 

 conjugation at first resembles tliat of Monocystis, but the actual 

 pairing-cells are bisexually differentiated into sperms in the one 

 parent, and oosplieres in the other ; it is remarkable that here the 

 pear-sha[)ed sperms are apparently larger than the oospheres. In 

 rteroccphahis the chief difference is that the sperms are minute.^ 

 In all cases of spore-formation the epimerite is lost and the 

 septum disappears ; in this state the cell is termed a sporont. 

 Sometimes tlie epiplasm of tlie sporont forms tubes (" sporoducts "), 

 which project tlnough tlie cyst-wall and give exit to the spores, 

 as in Grcgarina (Fig. 32, C), a parasite in the beetle Blaps. 



Gregarines infest most groups of Invertebrates except Sponges 

 and perhaps Coelenterates, the only exception cited being that of 

 Epizoantlius glacialis, a Zoantharian (p. 406). They appear to 

 be relatively harmless and are not known to induce epidemics. 



The Coccidiaceae never attain so high a degree of cellular 

 ilifferentiation as the Gregarines, which may be due to their 

 habitat; for in the growing state they are intracellular parasites. 

 Their life-history sIjows a .double cycle, which has been most 

 thoroughly worked out in Coccidiidae by Schaudinn and Siedlecki 

 in parasites of our common Centipedes. We take that of 

 Coccidiitm schuhergi (in Lithohius forficcdus'),hegiYmmg^Nii\\ the 

 sporozoite, which is liberated from the spores taken in with the 

 food, in the gut of tlie Centipede. This active sickle-sliaped cell 

 (Fig. 34, /; enters an epithelial cell of the mid-gut, and grows 

 therein till it attains its full size (ft), when it is termed a 

 " schizont " ; for it segments (Gk. cr-xil^oi, " I split ") superficially 

 into a large number of sickle-shaped zoospores, the " merozoites " 

 (c), resembling the sporozoites. The segmentation is superficial, 

 so that there may remain a large mass of residual epiplasm. 

 The merozoites are set free by the destruction of the epithelium- 

 cell in which they were formed, and which becomes disorganised, 

 like the residual epiplasm. Each merozoite may repeat the 



^ Leger, Arch. Zool. Exp. ser. 3, x. and ser. 4, v. (1902-3) ; for a full discussion 

 of tiie relations of association and conjugation in Gregarines, see Woodcock in 

 Quart. Journ. Mkr. Sci. 1. 1906, p. 61 f. 



- A Lithobius is llgured in Vol. \ . p. 45. 



