THE FLEXIBLE CREEPERS. 
479 
Some very favourable observations on the animal, made when 
I could look down directly on tbe head in a vertical position, have 
revealed some organs, which are doubtless vehicles of sensation, 
though I can but very uncertainly conjecture their office and 
value. At the back of the head there are two very minute 
prominences, each of which is terminated by a tuft of bristles. 
These organs are very generally found in the wheel- animals, 
and are in many species much more developed, and more 
favourably situated for observation, than in this case. They 
appear to be tubular prolongations of the skin, within which 
a piston-like body moves to and fro, carrying at one end a 
tuft of bristles, which diverge when protruded from the tube, 
and attached by a muscular cord at the other end to the 
interior of the body. A nervous thread in some species is 
seen to pass from the brain to each tube. The organs may be 
considered as analogous to the antennae of insects, though 
even of these we are not quite sure of the function. 
In our Eosphora there is seen, seated in a central depression 
between these two antennae, a little wart, of which I cannot 
sug-gest the purpose. Directly at the front of the head, at 
the most advanced point of the animal, whether creeping* or 
swimming, there are placed two symmetrical round specks of 
opaque crimson pigment, which come out with great brilliancy 
when the animal is viewed under sufficient magnifying power 
by reflected light. Dr. Leydig refuses to allow these to be 
organs of vision, but from repeated examination of them I 
have no doubt that he is in error, and that Ehrenberg was 
right in considering them eyes. Besides these, however, there 
is another red speck, which is without dispute of a visual 
character. It is far remote from the two frontal specks, being 
situate within the transparent skin, but near it, on the dorsal 
aspect, at about one-fourth (following the curve of the back) 
of the distance from the front to the origin of the foot. To 
make my readers understand its relations, I must describe a 
highly interesting and very remarkable organ. 
In most of the animals which constitute this order, but 
seen with peculiar distinctness in the present subject, and in 
one which very closely resembles it in appearance, Notommata 
ciarita , — there is seen a great ovate sac passing from the front 
along the back of the head, and terminating* by a rounded 
extremity in the neck. This is occupied by turbid matter, 
and seems to be indubitably a brain ; though it is quite 
without parallel among invertebrate animals to find any such 
concentration of the nervous substance in a single organ. 
We are accustomed to consider this character as exclusively 
belonging to the vertebrate classes, and to mark then* superior 
position in the scale of being*; the most sentient, the most 
