M. Koidzumi 
289 
(2) Pyrsonympha modesta sp. nov. (Plate XIV, figs. 65 and 66). 
The individuals of this species resemble the young forms of the preceding, 
but show some differences in their shape and some other structures. They 
are fairly small in size, measuring 30-80 /x in length, and are commonly 
pear-shaped. The nucleus is oval or round, and is situated at the anterior 
end. The flagellar cords run almost straight, and the ridges on which they are 
situated are commonly indistinct, except in much twisted forms. The cords 
themselves are confined, at the anterior end, to one side of the body, the other 
being free from them. The axial filament is more slender than in any indi¬ 
viduals of the preceding species, and is always single. The endoplasm is 
usually clear, though it frequently contains globular bodies. A peculiarity of 
this form is that the body is often conspicuously twisted, with the anterior 
end bent back into a peculiar form, so that it resembles a screw (PL XIV, 
fig. 66). In such individuals the bare area—noted above—at the anterior end 
is seen to lie in the inner angle of the bend. 
Dividing forms are also rare in this form, and the process of division 
appears, as far as I could conjecture from my material, to be of a type identical 
with that of the preceding species. 
II. Dinenympha. 
This subgenus embodies a number of species, distinguished from the 
preceding forms by the shape of the body and the mode of arrangement of 
the axial filament. The body is slender and usually assumes the shape of a 
club or an elongated spindle, nearly oval in its cross-section: or it may be 
rather flattened and ribbon-shaped, showing more or less distinct edges at 
both sides. The body is twisted and spirally wound in a characteristic manner, 
showing two to five undulations as seen from the side (commonly two or three, 
but four or five in some species). The body is less metabolic than in Pyrso¬ 
nymjpha , though abnormally thickened and shortened forms are met with 
rarely in some species. Such individuals may resemble small forms of Pyrso¬ 
nympha , but are easily distinguished from the latter by the characteristic 
feature of the axial filament. 
The degree of development of the axial filament varies in different species. 
In some it is thick and distinct, while in others it is quite slender, indistinct, 
and even almost unnoticeable in some species. In some forms it is almost 
uniform in thickness throughout its entire length; in others it gradually 
diminishes in thickness towards the posterior end, while yet in others it is 
indistinct in only the middle portion. The filament does not hang freely in 
the endoplasm, but its posterior end is fixed at the posterior extremity of 
the body. The axial filament is, moreover, usually adherent to the body wall 
for the greater part of its length, and it is not capable—as in Pyrsonympha — 
of independent lashing movements in the cytoplasm. In two species (D. leidyi 
Parasitology xm 19 
