84 W. G. RIDEWOOD AND H. T5. FANTHAM. 



purpose of iuvestigatiug the anatomical structure of this uew 

 species of Cephalodiscus, and these sections, and a few 

 additional ones cut more recently, were utilised for the study 

 of the Sporozoou. The sections were o fx, 6 fx, and 7*5 ju in 

 thickness. The majority of them were stained with Ehrlich's 

 h^ematoxylin and eosiu, the others with hasmatoxylin and 

 orange Gr, or Mayer's hajmalum, or borax caruiine. The 

 structural details of the parasite were most satisfactorily 

 shown by the sections that Avere cut from material fixed in 5 

 per cent, formalin and stained with hematoxylin and orange 

 Gr, or hsematoxylin and eosin. The parasites were studied 

 with a Zeiss 3 mm. apochi'omatic homogeneous immersion 

 objective, used in combination with compensating oculars 4 

 and 8, and occasionally 12. In some of the stages they are 

 of large size (pi. 6, figs. 1 and 2, iVsp.), and can be readily 

 recognised with a |- inch objective. 



OCCUKKENCE OF THE PaRASITE. 



The infection appears always to commence in the nervous 

 tissue, and although the parasites when at their largest may 

 project beyond the nerve layer into other tissues (pi. 6, 

 fig. 1, Ns^).), they remain in relation with nerve tissue at one 

 part of their surface. The parts of the nervous system in 

 which the parasite has been found are the central nerve mass 

 (pi. 6, fig. 2, NsiJ.), the nerve layer of the dorsal wall of 

 the buccal shield (practically a continuation of the central 

 tract), the nerve layer of the ventral wall of the shield 

 (pi. 6, fig. 1, Ns}-).), and the lateral nerve tracts near the 

 collar pores. The parasite has not been found in the nerve 

 tracts of the plumes, nor in those of the stolon. 



The occurrence of Neurosporidium in the nerve tracts 

 of Cephalodiscus is not the first instance of a Sporozoou 

 infecting nerve tissues, although infection of such tissues is 

 not common. Three instances are known of Neosporidia 



