48 INVERTEBRATE ANIMALS, 
reason they are often spoken of collectively as the “ stomatode,”’ 
or mouth-bearing Protozoa. The /uzfusoria may be defined as 
Protozoa which are provided with a mouth, and generally a 
rudimentary digestive canal. They do not possess the power of 
emitting pseudopodia, but are furnished with vtbratile cilia or 
contractile filaments. They are mostly microscopic in size, and 
their bodies usually consist of three distinct layers. They are 
mostly simple free-swimming organisms, but they sometimes 
form colonies by budding, and are fixed to some solid object in 
their adult condition. As types of these two sections of the 
Infusoria, we may take respectively Paramecium and Efpistylis. 
Paramecium (fig. 12, ¢, and fig. 13)is abeautiful slipper-shaped 
_ Fig. 12.—Morphology of Infusoria. a@ Efzstylis, a stalked Infusorian ; 4 A single 
cup of the same, greatly magnified, showing the ciliated digestive cavity, the 
contractile vesicle, and the smaller food-vacuoles; c Diagrammatic representa- 
tion of Paramecium, showing the funnel-shaped gullet, the nucleus and nucle- 
olus, food-vacuoles, and two contractile vesicles; d@ Aspidisca Lynceus; e Pera- 
nena globulosa, a flagellate Infusorian. 
little creature, which may be found commonly in stagnant waters 
or in artificially-prepared infusions. The body is nearly quite 
transparent, and consists of three layers—1, a structureless, 
transparent, external film or pellicle, called the “cuticle ;” 2, a 
central mass of soft semi-fluid sarcode, which is called the 
‘abdominal cavity,” as receiving the particles of food; and 3, 
an intermediate layer of firm and consistent sarcode, which is 
called the “cortical layer” (Lat. cortex, bark). The external 
membrane or cuticle is richly covered with minute vibrating 
hairs or cilia, which appear, however, to be really derived from 
the cortical layer. The cuticle is also perforated by the aper- 
