480 
POPULAR SCIENCE REVIEW. 
intelligent, the most vigorous among tlie Invertebrata, such as 
the Spiders and tlie Insects, having no such simplicity of 
nervous structure, but only a series of centres, in the form of 
ganglions, more or less distributed through the whole body. 
It must be borne in mind, however, that while, in the 
Rotifera, this brain is proportionally enormously large, and 
is quite alone — there being no other recognized concentrations 
of nervous substance than can be dignified with even the title 
of ganglions, — the neurine of which it is composed is in a 
very fluid condition; whence we may perhaps infer that its 
energies, whether for perception or will, bear no proportion to 
its volume. 
Upon this great brain-sac, at the point that approaches 
nearest to the skin of the nape, but always with a forward 
aspect, there is seated a wart, often large and conspicuously 
hemispherical. The summit of this rounded eminence is 
crowned with a mass of red pigment, at times scarcely per- 
ceptible, then suddenly becoming visible like a flush of crimson, 
rich in hue, translucent, but sometimes pale and ill-defined. 
Upon this there lies a convex lens, which can, in many species 
• — or, I should rather say, in many specimens of different species, 
for it is exceedingly variable and uncertain in this respect — be 
beautifully seen and clearly defined. 
There is, in some species, a very curious and remarkable 
organ, in close connection with the brain, the use of which is 
altogether unknown. It is very distinct in this Eosphora and 
in Notommata aurita, and in one or two other species of 
the latter genus. It is a sort of globular sac, of large size, 
occupying' the greater part of the bottom of the brain-sac, 
and sending up a rather wide tube through it. The globose 
extremity and a considerable portion of the tube are loosely 
filled with a substance, which, being’ opaque, appears dark 
when we view the animal by transmitted light ; but when 
reflected light is brought to bear on it — a ray of the sun, for 
instance — it comes out quite white upon the general trans- 
parency. Ehrenberg assumes that it is of the nature of chalk, 
and so has called it kalkbeutel, or chalk-sac ; but all that can 
with certainty be said is that it is a granular opaque white 
substance. 
The appearance and motions of this organ and its contents 
add greatly to the interest with which the microscopist views 
one of these creatures. It is so unique, so unaccountable, so 
conspicuous, so beautifully defined, so evidently connected 
with the seat of intelligence, and with the most obvious organ 
of sense, that it exercises a kind of fascination on the observer, 
who is induced to watch it, and to linger upon it, in hope of 
solving the problems which it suggests. There, however, it 
