34 
POPULAR SCIENCE REVIEW. 
vibrates in such, a way as to jerk the touching body with con- 
siderable force towards the centre of the contained area. 
The presence of animalcules, especially if active and highly 
coloured, such as those of the genus Microglena or Eaglena ,* in 
some abundance in the surrounding water, gives rise to an 
instructive and entertaining spectacle. One by one they 
quickly accumulate in the living trap, and a dozen or twenty 
may often be seen swimming* about in it, till one after another 
becomes engulplied in the deep cup-like mouth-funnel below 
the arms. When once they arrive here they rarely escape ; but 
the whole contents of the arm-trap are often lost at once by the 
sudden retraction of the animal into its case, when all the prey 
are left behind free to escape. Hence it appears that the victims 
are retained within the arms by the vortical current, produced, 
probably, by the cilia which line the mouth-funnel, whose action 
is persistent during the extension of the animal ; but that at the 
instant of retraction the ciliary vibration ceases, the vortical 
current is intermitted, and when the arms are chawn back the 
Monads remain where they were, there being in that instant 
nothing to prevent their passing between the tips of the arms. 
But when once the prey passes down below the area in ques- 
tion into the mouth-funnel, which is formed by very contractile 
walls, a slight constriction takes place in the neck, which has 
the effect of forcing the Monad down to the mouth of a capa- 
cious crop or proventricuhis (plate iii. b), which lies all across 
the upper part of the body. Here a sort of swallowing motion 
is seen, and the prey passes 'with a gulp down into the cavity. 
This crop is formed of thick granular walls, which run up 
in high processes on the dorsal and ventral sides to the bases of 
the arms. Within the ventral one of these processes, at its 
upper extremity, is inclosed a minute clear oval body, perhaps 
glandular. There is an irregular row of similar but smaller 
bodies running round the collar. An opaque, ill-defined, cloudy 
mass is seen on each side, evidently resident within the walls 
of the crop, in no wise produced or affected by its contents. f 
At the lower part and towards the dorsal side of this crop is 
placed the masticatory apparatus (plate iii. c), which consists 
of the ordinary jaws, evidently imbedded in the wall of the 
crop, working freely in its cavity without an enclosing mastax.% 
* These forms are considered by many observers to be “ protophytes,” or 
lowly organized plants. 
t Dr. Leyclig says the crop is furnished with four long bristles having 
hooked extremities, which appear, by their resistance to liquor potassce , to be 
chitinous. These I have not detected. 
X I have elsewhere given the name of mastax to the conspicuous muscular 
bulb, which in most Rotifera contains the jaws, and which answers to the 
true mouth in insects, &c. (See my memoir “ On the Manducatory Apparatus 
in the Rotifera,” in Phil. Trans, for 1856.) 
