440 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Genus NASSTJLA Ehr. ’33. 
(Dujardin ’41; Stein ’67; Cienkowsky ’55; Cohn ’66; Clap, et Lach. ’58; Kent ’81; Maupas ’83; Entz ’84; 
Fabre-Domergue ’88; Biitschli ’8S: Shevyakov ’96.) 
The body is ovoid or cylindrical, with well-rounded' ends, and in some cases slightly flattened. 
The mouth is ventral and placed some distance from anterior end (\ to J total length). A slight 
depression on the ventral surface marks the mouth region, which is further indicated by larger and 
more powerful cilia. The rest of the body is uniformly ciliated. The entire body is marked by clearly 
defined spiral stripes. The mouth is circular and the oesophagus is supported by a considerable 
armature, which usually extends dorsally and to the left, rarely to the right. In some cases the 
structure of this armature is indistinct; again it can be clearly seen to consist of definite rods (Stabchen) . 
The anus is probably always terminal. Contractile vacuoles are variable in different species. In some 
cases there is but one, which is placed at the posterior end or centrally on the ventral side; in others 
there may be four — two dorsal and two ventral. In many cases trichoeysts are uniformly distributed. 
Sometimes the body is colorless; again, and more often, it is brightly colored with red, blue, brown, 
or black pigment. The macronucleus is 
globular and central, occasionally band- 
form and with numerous attached micro- 
nuclei. Food substance varied, usually 
vegetable matter, see, however, below. 
Cysts are globular. Movement is a steady 
progression, combined with rolling. 
NassulamicrostomaCohn’66. Fig. 34. 
Synonyms: Paramcecium microstomum Cl. et 
Lach. ’58, Gourret et Roeser '88; Isotricha micrn- 
stomum Kent ’81. 
Body subcylindrical, rounded at each 
extremity, not quite twice as long as 
broad. A slight depression on one surface 
marks the position of the mouth, this 
depression being indicated by a row of 
longer cilia. The mouth is extremely 
small and is surrounded by a curious buc- 
cal armature. This is not made up of 
bars or rods, as in most species of Nassula, 
but appears perfectly smooth and uniform 
except for the considerable swelling at the inner end. The cuticle is firm and unyielding and marked 
by longitudinal and somewhat spiral rows of cilia and trichoeysts. Under the microscope this is one 
of the most pleasing forms found at Woods Hole. Its color is yellowish brown from the presence of 
brilliant particles of coloring matter held in the cortical plasm, and, as it slowly rolls along, these 
particles and the black trichoeysts give to the organism a peculiar sparkling effect. The macronucleus 
is almost central; the contractile vacuole posterior. The endoplasm appears well filled with food 
bodies, some of which could be distinguished as Arnphidinium and Glenodinium. 
Length 55 /< ; greatest diameter 30/« . 
' Genus CHILODON Ehr. 
(Dujardin ’41; Engelmann ’78; Stein ’54, 58; Kent ’81; Biitschli '88; Gruber ’83; Cienkowsky ’55; Mobius ’88; 
Clap, et Lach ’58; Wrzesniowski ’65; Shevyakov ’96.) 
Small forms, greatly flattened dorso-ventrally and almost egg-form in outline. The anterior end 
is bent distinctly to the left and forms a characteristic process, which, together with the entire margin 
of the body, is soft and flexible. The posterior end is, as a rule, broadly rounded. The ventral surface 
is finely striate, and this surface alone is ciliated. The lines of cilia converge at. the mouth, and at this 
region the cilia are somewhat larger and more distinct, thus forming a functional adoral zone. The 
mouth is median and is situated in the anterior half of the body. It is surrounded by a well-defined 
armature, composed usually of from 10 to 16 rods. The contractile vacuoles are quite varied and from 
one to many iu number, the number increasing with the size of the individual. The macronucleus is 
' /'VTT TT 
Fig. 34. — Nassula microstoma. 
