ON POLYPI. 575 
and he arrived at this result, that the movements of these 
animals were in accordance with those of the barometer. 
The actiniz possess no maleficent quality, and are eaten 
in several countries. 
Dr. Spix has given some very curious details respecting 
the organization of these animals, which he observed and dis- 
sected upon the coasts of the channel. 
In considering the gelatinous polypi, we shall confine our 
remarks chiefly to the HYDRA. . 
The hydre are animals exceedingly simple, which we can 
scarcely compare to any thing but filaments of small thick- 
ness, fixed at one of their extremities, by means of a sort of 
sucker, and provided on the other with a crown of cirrhi, or 
tentacula, more attenuated than the finest hairs, to the num- 
ber of ten or more, and possessed of extreme contractility. 
This disposition of the tentacula and even their uses, caused 
these little animals to be compared to the polypi of the an- 
cients, now denominated octopus, and occasioned Reaumur to 
give them the name of polypi. The structure of the different 
parts of the body of the hydre is throughout completely uni- 
form. In fact, we discover in them, even with the assistance 
of the microscope, nothing but a sort of parenchyma, formed 
of globules, and cellular tissue, and which is capable of con- 
traction, particularly in the tentacula, to such a degree as to 
disappear almost completely. Accordingly, the general sen- 
sibility of these animalcule is exquisite, so that they can feel 
or perceive the light, and distinguish it from the shade; not 
that we would be understood to say with some writers, that 
they actually possess the power of vision, through the medium 
of the general envelope ; but they are in the predicament of 
plants, which direct themselves towards the light, the effects 
of which they experience, without otherwise perceiving the 
bodies which transmit it. The hydre have no traces of the 
