FORMATION OF THE PSEUDONAVICELLA. 193 



the conjugation has taken place, the two bodies are still distin- 

 guishable within the wall of the cyst (Fig. 96, A), after this the 

 contents, either as a whole or in their outer layer, produce by a 

 sort of peripheral segmentation a large number of small balls, which 

 become the spindle-shaped Pseudonavicellae after the secretion of a 

 hard shell (Fig. 96, B). 



We cannot here discuss the numerous more or less striking differ- 

 ences in the form and size of these spores. We must, however, point 

 out that the cysts sooner or later find their way to the exterior (though 

 often, as in the earthworm, only after the death of their host), and 

 there set the spores free. For this last purpose there are sometimes 

 special arrangements in the cysts, such as canals and " discharging 

 bombs," which are formed out of that portion of the contents which 

 was not devoted to the manufacture of spores. 1 



Each Pseudonavicella contains a granular mass, which, after secret- 

 ing a clear plasma, very soon gathers itself into a central mass. 

 According to Lieberkiihn, who bases his statement on investigations , 

 into the Gregarine of the common earthworm (Monocystis agilis s. 

 lumlrici), this mass forms an amoeboid creature, which breaks out of 

 the Pseudonavicella, remains for a while in the body-cavity of its host, 

 and finally becomes a Gregarine by the assumption of a cuticle. 2 



It is, however, hardly doubtful that Lieberkiihn has fallen into 

 error. He has confused amoeboid masses found in the perivisceral 

 fluid of the earthworm, and representing blood or lymph corpuscles 

 with stages in the life-history of the Gregarine. He has also further 

 erred in regard to the changes which the contents of the Pseudo- 

 navicellse undergo, for, especially in the case of Monocystis luiribrici, it 

 is certain, as Schneider has stated, that the development is quite 

 otherwise. The contents, instead of forming an amoeboid body, fall into 

 about six little clear sickle-shaped rods. These distribute themselves 

 equally over the two halves of the Pseudonavicella, and the rest 

 of the granular mass collected into a ball lies between them (" nucleus 

 de reliquat"). (Fig. 97, A-C.) The same changes take place also in 

 many other Gregarines, usually, however, not in the original host, 

 but externally. The expelled cysts may be kept alive for some weeks 

 in water (Fig. 97, D-F). 



Since Schneider succeeded, after treatment with osmic acid, 

 in demonstrating the presence of a nucleus in the sickle-shaped 

 bodies, he supposes that they are already true Gregarines, and that 

 they pass without essential change, by growth, accumulation of 



1 Aime Schneider, " Sur un appareil de dissemination des Gregarines," Comptts 

 rendus, t. Ixxx., p. 432, 1875. 



2 " Evolution des Gregarines/' Mem. couronn. de VAcad. de Belyc, t. xxvi., 1855. 



N 



