INFUSORIES. 39 
structure. Some, in which no oral! aperture can be found, must 
receive nutriment by means of absorption through the external 
surface alone. Others have a mouth, usually surrounded by cilia, 
by the motion of which a current is produced in the water, carrying 
the food which it may contain to the mouth. The subsequent 
transmission of nutriment throughout the body is effected in spaces 
of a vesicular form—which contract again when their contents have 
been expelled: they are pushed on by others that have more lately 
come into view, and have motions that cannot be reconciled with 
the notion that they possess proper walls. We must rather suppose 
therefore that these vesicular spaces are excavations in the gelatinous 
tissue of the body. The undigested portion of the food is, in many 
of these creatures, cast off by another aperture’ of the body: in 
others it escapes through the same opening by which it was received. 
Special organs of Respiration have not been recognised. The 
external surface of the body appears to be the seat of that function. 
Still less are there any blood-vessels: perhaps those spaces, which 
in many species are seen to contract and expand, and which are 
various in form and number, may serve for moving and transmitting 
the nutrient fluid which supplies the place of the blood’. 
Although no muscular fibres* are present, these animals possess 
the power of motion in a great degree. Some move slowly, others 
very nimbly. As organs of motion the greater number have cilia. 
In some are produced by contraction all sorts of changes in the 
1 [STEIN considers all ciliated infusories without a mouth to be larval or embryotic 
forms of other creatures. Die Infusionsth. s. 181.] 
2 [According to STEIN there is no ready-formed anal opening in any infusory. In 
those families which do not reject their excrement by the mouth, it is forcibly pressed 
through the integument of a determinate region of the body, more or less extensive, and 
not sharply defined. After the exclusion, the rupture is completely closed again. It 
is allowable, therefore, to speak of an anal region, not of an anal aperture. Die Infu- 
sionsthiere. p. 24. | 
3 EHRENBERG holds these contractile spaces, or vesicles (?), to be vesicule seminales. 
The ¢esticulus is with him a structure whose connexion with these vesicles he has not 
demonstrated, and which vy. SIEBOLD regards as a nucleus, whilst he compares the 
entire infusory to an organic cell. 
* In the hollow pedicle of Vorticella, and other similar genera, there is a longitudinal 
muscle which by its contraction effects the spiral retraction of this part. EHRENB. Die 
Infusionsth. s. 270. [CZERMACK denies that the contractile streak in the canal of the 
stem is a muscle: see SIEBOLD and KOLLIKER’s Zeitschrift fiir wissenschaftliche Zoolo- 
gie, IV. 442. Also see STEIN, op. cit. p. 81.] 
