564 SUPPLEMENT 
still more intense. The caustic quality of this humour is not, 
however, always in accordance with the phosphorescent pro- 
perty, since there are species which are not luminous, but 
which, nevertheless, produce a sting. 
These animals are in general perfectly colourless, and re- 
semble the purest and most transparent rock-crystal. ‘There 
are some, however, which have coloured parts, reddish, fine 
ultra-marine blue, greenish, &c. 
The apparatus of sensation in the medusa appears to be 
limited to the skin. The name of tentacula, which has been 
given to the filaments, more or less elongated, which border 
the umbrella, the use assigned to them, as well as the brachial 
appendages in certain species, might cause it to be suspected 
that these organs enjoy a more exquisite sense of touch. But 
there is nothing in the organization of these parts to confirm 
this suspicion, and it is not even certain that these organs 
serve for the uses which are attributed to them. 
No trace of nervous system has ever been observed in these 
animals, nor is it probable that any exists. 
If, after investigating the organization of the medusz, we 
turn our attention to the study of their functions, we shall 
still find many other phenomena equally worthy of obser- 
vation. 
Their general sensibility appears to be extremely obtuse ; 
and, perhaps, it is the same with the special sensibility of 
the marginal and buccal tentacula, whose power of contracti- 
lity, however, appears to be very great. The meduse do not — 
seem to feel the hand that seizes them. 
Their locomotion, which is very slow, and denotes a very 
feeble degree of muscular energy, nevertheless, appears to 
have no cessation, since, being of a specific gravity more con- 
siderable than that of the water in which they are immersed, 
these animals, so soft, that it is probable they could not rest 
upon a solid ground, are obliged to move incessantly to sus- 
a 
