SPOROZOA : SARCO-, MVXO-, SPORIDIA. 863 



which they are lodged are detached they become ovate. Balbiania is 

 sub-spherical. 



There is a membrane, either delicate (Miescheria> Balbiania), or com- 

 posed of close-set rods (Sarcocystis). The contents are gelatinous, proto- 

 plasmic, with a number of minute, refractile, fatty (?) granules and 

 protoplasmic corpuscles or germs (?). Rotation round the longer axis 

 and contractions have been observed in a Miescheria of the Pig by 

 Waldeyer. In large specimens the contents, except at the two ex- 

 tremities, are broken up into a number of spores (?), polygonal from mutual 

 pressure, but globular when set free. The polygonal bodies contain large 

 numbers of reniform or semi-lunar germs, which in Balbiania at any rate 

 are developed in the peripheral bodies at an earlier period than in the 

 central, and are set free by the breaking down of the inclosing membranes. 

 This is probably the case also in the two other genera. The germs are 

 homogeneous or granular, and often contain a bright spot or vacuole at 

 either extremity. The vacuoles have been said not to exist in fresh 

 germs. No nucleus has been detected either in the germs, the bodies 

 within which they are formed, nor in the parent organisms. 



The Sarcosporidia are sometimes spoken of as ' Miescher's vesicles,' 

 or ' Rainey's corpuscles,' the names of their first discoverers in Germany 

 and England respectively. 



(iv) Myxosporidia. The Sporozoans known by this name are para- 

 sitic in various freshwater Fish and certain Elasmobranchii. The skin 

 of the head and opercular cavities, the branchiae and viscera are the 

 commonest localities ; the muscles of the body are seldom infected, and 

 the central nervous system is completely exempt. They are sometimes 

 found in delicate cysts with nucleated walls, probably derived from the 

 tissues of the host, ranging in size from about J in. downwards, but the 

 Myxosporidium of the Pike's urinary bladder lives free on the surface of 

 the mucous membrane. The organism is Ameeda-like, more or less rounded 

 or elongate ; it shows a distinct division of exoplasm and endoplasm. 

 The surface of the exoplasm may be covered completely or partially with 

 fine, simple, or branched retractile processes. The endoplasm is granular, 

 sometimes coloured with yellow or brown fatty granules, and crystals of 

 haematoidin : it is multinucleate. Movement may be slowly effected by 

 lobose pseudopodia. Spore-formation commences at an early period, and 

 is perhaps a continuous phenomenon. The number of spores present is 

 variable. Their development has been traced in the Myxosporidium in- 

 habiting the Pike's bladder. Clear globules of protoplasm make their 

 appearance in the endoplasm, containing six nuclei apiece. A delicate 

 membrane appears round each of them, and then each divides into two 

 tri-nucleate halves, the spores, which become fusiform. Two of the nuclei 



