No. I.] TWO NEW GREGARINIDA. 9 
prise, I discovered a very large gregarine belonging to the order 
Polycystidea. After this I naturally examined every specimen 
of Rhyncobolus that came in my way; but I found that the 
parasitized worms were rare,—perhaps 10% of those examined, 
—and even these contained only a few gregarines, seven or 
eight at most. 
This gregarine is generally found with its anterior, that is, 
the larger, end (PI. III, Fig. 37) buried in the wall of the host's 
intestine, and its posterior end projecting out into the intestinal 
canal. It is easily distinguished from its surroundings, appear- 
ing as a white opaque body about 0.7 mm. in length. 
The body of the parasite is composed of an exceedingly large 
deutomerite (Pl. III, Fig. 37, dew’mer), containing the nucleus 
in its anterior portion, and a small protomerite (f7’mer), which 
bears an epimerite (e’mer). 
Its surface is covered with fine longitudinal striations (PI. III, 
Figs. 37-39) due to longitudinal folds in the cortical layer of the 
body (Pl. III, Figs. 41, 42). On focusing just below the surface, 
cross striations can occasionally be seen (PI. III, Fig. 37); they 
are due to circular muscular fibres. In optical longitudinal sec- 
tions of the parasite they are seen along its edges as black dots 
(ETL, Pizs..37,.38)- 
The outer cuticular wall appears very thick in longitudinal 
sections (Pl. III, Fig. 40); but this appearance is misleading, as 
cross sections of the parasite (Pl. III, Figs. 41, 42) clearly show. 
It is produced by the peculiar relation of the circular muscle fi- 
bres to the relatively thin cuticular covering and to the cortical 
portion of the parenchyma, which lies immediately below the 
cuticula. At short and tolerably regular intervals the circular 
contractile fibres come nearer to the deep surface of the cuti- 
cula and apparently have here a closer connection with that 
structure than over the intervening regions. The result is 
that the subcuticular layer of the parenchyma is thrown into 
longitudinal ridges, separated by sharp, deep furrows. The 
height of the ridges and the narrowness of their bases are to a 
certain extent dependent on the degree of contraction of the 
muscular fibres. The more the muscles shorten, the thinner 
and higher are the ridges. These ridges are so numerous and 
