THE SPOROZOA 161 



("falciform body," " Sichelkeim "). The protoplasm of the sporo- 

 zoites is finely granular, and when they are formed, a surplus of 

 coarsely granular protoplasm is left over from the sporoplasm as 

 the sporal residuum ("reliquat sporal"). The fully-formed spore 

 has in Monocystis the form shown in Fig. 7, C ; it is more or less 

 boat-shaped, and resembles a diatom of the genus Navicella, whence 

 is derived the name pseudonavicella, by which Gregarine spores have 

 long been known. The sporocyst is slightly thickened at each 



Fio. 7. 



Development of the spore of Mono- 

 cystis, A, oval sporoblast with single 

 nucleus (a). B, the sporoblast has 

 secreted the sporocyst at its surface, 

 and the sporoplasm within it has 

 become contracted and diminished 

 in volume. C, ripe spore with eight 

 sporozoites and residual protoplasm 

 (6). D, diagrammatic cross-section to 

 show the arrangement of the sporo- 

 zoites round the central residual pro- 

 toplasm. (After Biitschli, from 

 Lankester.) 



pole, and within this very resistent and impervious envelope the 

 eight sporozoites are packed lengthways round the centrally placed 

 sporal residuum. During the formation of the spores the cystal 

 residuum is slowly absorbed, and the ripe cyst contains only a 

 great number of the pseudonavicellae, not arranged in any definite 

 pattern (Fig. 8). 



The above account of the conjugation and spore - formation is that 

 given recently by Cuenot, whose researches confirm the discoveries of 

 Siedlecki with regard to an allied form Lankesteria ascidiae (Lank.), and 

 are in harmony with the still more recent account given by Leger [23] 

 for Stylorhynchus. Cuenot's description of the spore-formation and the 

 events antecedent to it is confirmed in all essential details by Cecconi [11] 

 and Prowazek [2 5 a]. Previous to Cuenot the reproduction of Monocystis 

 had only been studied by Wolters [29], whose description of the process 

 is very different. According to Wolters the association of the two full- 

 grown trophozoites or sporonts within the cyst is a true conjugation, 

 similar in its details to that known in Actinophrys from the researches 

 of Schaudinn. Wolters describes the nucleus of each sporont as dividing 

 mitotically to form two nuclei, one of which is given off in a polar body, 

 while the other remains as a pronucleus. The two nuclei are then stated 

 to travel towards the septum formed by the apposition of the cuticular 

 body-walls of the two sporonts, and at one point the septum becomes 

 dissolved, permitting the fusion of the pronuclei into a single nucleus. 

 After a time the fusion -nucleus divides into two nuclei, which then 

 rapidly divide up to form numerous small nuclei, round which the proto- 

 plasm of the sporonts becomes segmented to form the sporoblasts. From 

 the sporoblasts the spores are formed as above described. 



It is unfortunate that these statements of Wolters, which seem to be 



ii 



