SUBKINODOM PROTOZOA. 27 



when not so enclosed seem to possess tlie power of slow 

 amoeboid movement. The endoplasm is usually well differ- 

 entiated from the ectoplasm and contains in the adult condi- 

 tion a large number of minute nuclei. 



Reproduction by division is not known to occur, spore- 

 formation being the only method as yet observed. In the 

 Myxosporidium occurring in the urinary bladder of the 

 Pike the protoplasm breaks up into a number of spherical 

 masses each containing a number of nuclei. The fate of 

 all of these masses is not known, but some, containing only 

 six nuclei, form a wall about themselves and divide into 

 two portions each of which contains three nuclei. These 

 trinucleated bodies elongate, develop a wall, and become 

 pseudonavicella-like spores, one of the three nuclei per- 

 sisting as the spore-nucleus, while the other two, situated 

 at the extremities of the spore, seem to give rise to a sac-like 

 structure containing within its interior a spirally rolled fila- 

 ment which is emitted when the spore is subjected to press- 

 ure and probably serves for the fixation of the spore to the 

 body of a host. The further history of the spores is not 

 thoroughly known, but it seems probable that the contents 

 escape as amoeboid masses which develop into adult Myxo- 

 sporidia. 



In many respects the Myxosporidia resemble closely the Q-regarinida, 

 but the possibility of their being in reality not of an animal but of a 

 plant nature must not be overlooked. By some authors their nearest re- 

 lations have been found in the Myxomycetous and Chytridiaceous fungi, a 

 view which certainly has not a little to recommend it. 



3. Order Sarcosporidia. 



The Sarcosporidia are, with a single exception, parasites 

 in the muscle-tissue of warm-blooded animals, especially 

 of Mammalia, being found in the interior of the primitive 

 fibrils of the striated muscles, whose contents they more or 

 less destroy. 



They form somewhat elongated sacs 1-2 mm. in length, 

 the wall of the sac being formed of a distinct membrane 

 which has the appearance of being covered with fine bristles. 

 The contents of the sac consist of a protoplasmic ground- 



