252 SCIENCE PROGRESS 



contents or cytoplasm of the Lencocytozoon are usually granular ; 

 the granules take up stains very easily, and thereby the nucleus 

 or controlling apparatus of the cell, which lies beneath these 

 granules, is frequently obscured. The nucleus often lies nearer 

 one end of the parasite than the other (fig. i,a, b). Contractile 

 threads or myonemes are present in the outer layers of the 

 protoplasm of the body of L. musculi (fig. 3, b), but these have 

 not been recorded in other forms. The myonemes are the 

 agents of locomotion whereby the parasite is enabled to change 

 its position and to progress backwards or forwards in the 

 plasma of the blood. 



The parasites living within the leucocytes (cytozoic forms) 

 vary more in appearance than do the free organisms, because 

 they naturally adopt the form most suitable to a limited space. 

 Further, twisting of the parasite on itself occurs, resulting in a 

 thin-edge or tailed appearance. Wenyon (1906) has described 

 a U-shaped form of the parasite discovered by Gerrard in the 

 polymorphonuclear leucocytes of Malay dogs. Judging from 

 the observations of other workers, this is a somewhat rare form. 

 Polymorphonuclear leucocytes (fig. 1, a) naturally afford greater 

 opportunities for irregularity in shape than do mononuclear 

 forms (fig. 1, b, c, d). 



IV. Movements 



The movements of Leucocytozoa have been most fully described 

 in the case of L. musculi. The movements of the small forms 

 (merozoites or young daughter-forms) are very slight. On the 

 surface of the body of L. musculi myonemes are present, though 

 these have not been described in other forms. By the contraction 

 •of the myonemes, the two ends of the parasite are approximated, 

 then, by a sudden wave of relaxation, travelling from the 

 posterior towards the anterior end, the organism is straightened, 

 and at the same time is propelled forwards. As the organism 

 moves forwards, it also rolls from side to side and partially twists 

 on itself. The path of the parasite is never straight and is 

 frequently very restricted. The movements of these small 

 forms are much more active when the parasite happens to be in 

 the neighbourhood of a leucocyte, and they are terminated 

 as such when the parasite penetrates the blood cell. Intra- 

 corpuscular existence involves movement in a much denser 

 medium and avoidance of still denser portions of the cell 



