416 



THE PROTOZOA 



characteristic of Microsporidia generally. Its most important variations are 

 exhibited in the mode of spore-formation and in the vegetative or multiplicative 

 stages. Only in the genus Nosema does the sporont give rise to a single 

 spore. In Thelohania chcrtogastris, studied by Schroder (781), for example, 

 the sporonts are distinguished from the meronts by being enclosed in a 

 delicate cyst, within which the sporont multiplies by successive divisions 

 into eight uninucleate sporoblasts (Fig. 173), connected at first by a central 

 mass of protoplasm like a rosette ; but as soon as the sporocyst is formed 

 the sporoblasts become separate. The nucleus of each sporoblast divides 

 until there are five, two for the amcebula, one for the polar capsule, and two 

 for the sporocyst, and the development is similar to that of the spore of 

 Nosema bombycis already described. 



A noteworthy feature of many Microsporidia is that the spores formed are 

 of two sizes, rnicrospores and macrospores, which may differ considerably in 

 their dimensions. In Pleistophora longifilis the macrospores are 12 M in 

 length by 6 M in breadth, while the microspores are 2 or 3 /* in length and 

 broad in proportion (Schuberg). It is very probable that these differences 

 are related to differences in sex of the contained amcebulae, and that the two 

 kinds of spores produce macrogametes and microgametes respectively. 



H 



FIG. 173. Stages in the spore-formation of Thelohania chcetogastris. A, Uni- 

 nucleate sporont ; B, C, division of its nucleus into two ; D, E, F, G, division 

 of the nucleus and body into four ; H, division into eight sporoblasts ; /, eight 

 sporoblasts, each with the nucleus dividing again ; J, two sporoblasts from a 

 clump, showing further divisions of the nuclei ; K, young spore showing two 

 parietal and three central nuclei (nucleus of the capsulogenous cell and two 

 nuclei of the amoebula). After Schroder (781). 



In Pleistophora periplanetce, according to Shiwago, several planonts 

 (" amoeboids ") fuse into a plasm odi um ; their nuclei become resolved into 

 chromidia which become mixed together a process interpreted by Shiwago 

 as chromidiogamy. From the chromidia secondary nuclei are formed, which 

 become the nuclei of the sporonts (" daughter-am ceboids "). The sporonts 

 become free from the plasmodium and form spores. If this account be con- 

 firmed, it is clear that the alleged autogamy of the Microsporidia, if it occurs, 

 is not necessarily an autogamy without amphimixis. In Thelohania mcenadis, 

 according to Perez (778), the nucleus of the sporont becomes resolved into a 

 cloud of chromidia, from which the eight nuclei of the sporoblasts are recon- 

 structed. 



The greatest difference in the vegetative phase from the condition described 

 for Nosema bombycis is seen in the genus Ohigea, where the multiplication of 

 the meront leads to the formation of a multinucleate plasmodium a result 

 easily explained on the supposition that the nucleus of the meront divides 

 repeatedly, but the body as a whole does not do so. In this way a relatively 

 large plasmodial trophozoite, comparable to that of the Myxosporidia, is pro- 



