THE NEOSPORIDIA 



425 



uninucleate sporonts (" pansporoblasts ") towards the centre or at one 

 pole, while the peripheral zone or the opposite pole remains in the 

 plasmodial condition. The sporonts grow in size, and at the same time 

 multiply by repeated fission to form a cluster of about sixteen spores, 

 a " spore-morula " (Fig. 177, B), enclosed by a membrane. Between 

 the spore-morulae an indefinite framework is formed by the residual 

 protoplasm in which the sporonts have developed (Beattie). Hence the 

 full-grown parasite exhibits three zones, which may be concentric or polar 

 in arrangement : a plasmodial region, peripheral or polar ; an intermediate 

 zone of spore-formation; and a central or polar region containing ripe 

 spore-morulae. The process of spore -formation continues until the whole 

 cyst is full of spore-morulae. The ripe cysts burst and scatter their 

 contents in the tissues. It is possible that spores set free in this way 

 may germinate in the tissues and give rise to fresh cysts ; but it is more 

 probable that the spores, if they 

 escape the phagocytes, are dis- 

 charged from the surface of the 

 epithelium. Prom the analogy of 

 other Neosporidia, it is reasonable 

 to suppose that the youngest uni- 

 nucleate forms of the parasite are 

 the multiplicative phase in the 

 tissues, and that the spore-morulae 

 represent the propagative phase. 

 Nothing is known, however, of the 

 mode of transmission of the para- 

 site or of the manner in which the 

 infection is acquired. 



A parasite is described by 

 Laveran and Pettit from Salmo 

 irideus, which in the opinion of 

 the authors presents affinities 

 with Rhinosporidium and Neuro- 

 sporidium. It causes a disease 

 in the fish, termed in German 

 " Taumelkrankheit." 



B 



Fio. 177. Rhinosporidium kinealyi. A, 

 Segment of a section through a cyst : 

 e., hyaline envelope ; p.z., peripheral 

 zone of pansporo blasts ; t'.z., inter- 

 mediate zone of pansporo blasts contain- 

 ing a few spores ; c.z., central zone of 

 ripe spore-morulse; B, ripe spore-morula ; 

 m., membrane ; ap., spores. After 

 Minchin e.nd Fantham. 



In addition to the more or less 

 typical genera of Haplosporidia 

 mentioned in the foregoing para- 

 graphs, a number of other forms 

 have been described, of which the 

 affinities and systematic position re- 

 main for the present uncertain. Such are the " Serumsporidia " of Pfeiffer, and 

 other forms, for a review of which the reader must be referred to the comprehen- 

 sive memoir of Caullery and Mesnil (802) or to the original descriptions. The 

 remarkable form, Schewiakovetta schmeili, however, presents peculiarities which 

 deserve special mention. It is a parasite of the body-cavity of Cyclops spp., 

 and was the subject of detailed study by Schewiakoff. In the active con- 

 dition it occurs as an amoeba with a single nucleus and a contractile vacuole, or 

 as a plasmodium formed by fusion of such amoebae. Encystment of either the 

 amoebae or the plasmodia occurs, and within the cyst a number of simple, 

 uninucleate spores are formed, which, although possessing a distinct envelope, 

 multiply further by fission, with mitosis of the nucleus. Germination of the 

 spores sets free small amoebulae. In many points this form is unique amongst 

 the Sporozoa, and should perhaps be classed rather with the parasitic 

 amoebae. 



Incertce <Sft. In conclusion a number of forms must be mentioned which 

 have been referred to the Neosporidia, but of which the position and affinities 

 are quite doubtful. 



