450 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
may be widely spread, limited to the posterior region, or arranged in a girdle about the middle. The 
contractile vacuole is simple, and posterior in position. The macronucleus is spherical and usually 
central in position. Movement is rapid swimming, combined with resting and floating periods, the 
latter usually terminated by a sudden leap. 
Fresh and salt water; more common in the latter. 
PStrombidium caudatum Fromentel ’74. Fig. 46, a, b, c. 
Fromentel described a fresh-water form of this genus with a caudal appendage. The body is 
pyriform, broadly truncate on the anterior end, in the middle of which rises a papilliform process 
{Schnabel) . On this process is a heap of pigment granules, which, however, are not constant. A ring 
of long cirri surround the anterior end and pass into the peristome, and from the left edge of this line 
of cirri a large adoral zone continues down to the mouth. The peristome is elongate and sac-form, 
and the mouth lies at the posterior extremity. With the exception of a caudal filament there are 
no other motile organs; this is about half as long as the body, structureless, hyaline, and sharply 
pointed. It splits up into a bundle of tine fibers upon treatment with caustic potash (c). The cirri 
emerge from minute hollows in the edge of the anterior border. The cortical plasm contains peculiar 
rod-like bodies, which look more like lines or markings than like rods or trichocysts. The nucleus is 
large, spherical, and placed in the center of the body. The contractile vacuole is posterior. 
Length without appendage is about 35 ju; greatest diameter 15 to 18 /i. In decaying vegetable 
matter. Common. 
Although Fromentel’s species is incompletely described, it is very evident that the organism corre- 
sponds fairly well with the Woods Hole variety. His was a fresh-water type; this is marine, but the 
caudal filament and the contractile vacuole are similar. Certainly in this case the organism can not 
be regarded as a Vorticella broken off its stalk, as Kent ’81 suspected. The anterior process with its 
pigment spot; the cirri, the spherical nucleus, the position of the vacuole, etc., are all opposed to such 
an interpretation which Kent applied to the original species. Neither can it be a Tintinnoid. I place 
it provisionally as S. caudatum. 
