ON THE ORGANS OF RADIATED ANIMALS. 
125 
roots of the tentacula, embedded in a strong circular band of muscular fibres 
which surround the orifice of the stomach, and act the part of a powerful 
sphincter in closing the aperture.” Professor Grant adopts the description of 
Spix, without stating whether he has verified by his own dissections the descrip¬ 
tion of the Bavarian naturalist. The question, therefore, appears to be an 
“ open” one, and it is to be hoped that individuals favourably located for studying 
this interesting class of animals will turn their attention to the subject. 
The ocean of every clime swarms with innumerable forms of Arachnoderma, 
varying in size from microscopic atoms, like the Polygastrica , to those large 
masses of Sea-jelly ( Medusa ) that are left on every shore by the receding tide. 
In the stillness of night the mariner s solitary path through the trackless deep is 
oft illuminated by the phosphorical light emitted by these simple beings, some 
resembling an undulating plume, whilst others bespangle the vessel’s track with 
luminous spots, or convert the entire surface of the deep into a sheet of pale 
light. When we attempt to unravel the mechanism by which these wonderful 
phenomena are produced, we find to our astonishment that these beings are 
composed of little else than a mass of cellular tissue, which when taken from the 
water rapidly gives off by evaporation the fluid contained in its interstices, and 
leaves behind only a few shreds of dried membrane, which, from an animal 
weighing when alive a few pounds, will scarcely amount to as many grains—so 
true is the remark made by the industrious Peron, when speaking of the 
Medusce :<—“Among the animals of this family, we find the most important 
functions of life performed in bodies which offer to the eye little more than a 
mass of jelly. They grow frequently to a large size, so as to measure many 
feet in diameter; and yet we cannot always determine which are their organs of 
nutrition. They move with rapidity, and continue the motion for a long time; 
and yet we cannot always satisfactorily demonstrate their muscular system. 
Their secretions are frequently very abundant, yet still the secerning organs 
remain to be discovered. They seem too weak to seize any vigorous animal, and 
yet fishes often constitute their prey. Their delicate stomachs appear to the 
observer incapable of digesting such aliment, but it is nevertheless dissolved in a 
very short space of time. Most of them shine with great brilliancy by night, 
nnd yet we know little or nothing of the agent that produces so remarkable a 
phenomenon, or of the organs by which the luminous matter is elaborated. And, 
lastly, many of them sting the hand that touches them, but how or by what 
means they do so still remains a mystery.” 
This eloquent description of the Acalephce will suffice to shew that the study of 
the peculiar nature of the tissues of this class, the singular disposition of their 
organs, and the anomalous character of the functions they perform, opens as wide 
