232 Gilruth, Sweet, and Dodd : 



larity from other species of this genus, apart from the point that 

 it seeniiS to be the only phismodial form recorded from the 

 order Anseriformes of Birds. 



These parasites were found in two specimens of Musk Duck 

 obtained at different times. Very few cells were affected, so 

 that often none could be seen in many consecutive " fields." 

 The size of the normal erythrocyte is 1.3.5 to 14.2 fx long by 7.8 

 to 8.5 IX. wide. The parasite varies in size from 8.5 to 10 /x 

 long by 4.8 to 9.7 /x wide in apparently fully-developed forms, 

 thus causing an increase in size and a distortion of the infected 

 erythrocytes, which may reach 15.6 /x long and 9.7 to 10.6 /x 

 wide in size, and become irregular, pyriform, polyhedral, or 

 spherical in shape. 



Both young forms (cf. Figs. 7, 8 and 12) and mature gameto- 

 cytes were foimd (cf. Figs. 3, 9, 13, 14 and 15). In the young 

 parasites which are elongated, e.g.. Fig. 7, no nucleus could 

 be seen, but numerous fine granules of pigment are present. 

 Later, as in Fig 8, large melanin-pigment granules appear, this 

 figure also illustrating their occasional triangular form. In 

 the one shown in Fig. 12, a small well-defined vesicular nucleus 

 can be seen. The later stages show a gradual approach to the 

 spherical form found in the mature parasite, e.g.. Figs. 3, 9, 13, 

 14, 15. With the increasing size and more spherical form of 

 the parasite, the nucleus of the host-cell becomes displaced 

 from the centre and pushed more or less to one end or side. 

 In tiie former case, the direction of the long axis of the nucleus 

 is changed, and it comes to lie obliquely across the length of 

 the erythrocyte much in the same way as happens in the host- 

 cells of Proteosoma praecor. No bean-shaped or gregarinoid 

 forms similar to those in F. praccor could be found, unless the 

 form shown in Fig. '6 uuiy be so regarded. The spherical shape 

 of the gametocytes reminds one of those of P . passeris. but the 

 parasites of the Musk Duck are larger than those of the spar- 

 row, being really intermediate in size between P. vaughani 

 and P. passeris 5 to 6.5 /x), and P. majoris (11 to 12 /x). 



Both nude and fenuile gametocytes are present, but no 

 sporulation stages could l)e found. The male gametocytes are 

 represented by Figs. 14 and 15, in which the body of the 



