864 RADIATA. 
tendinous lines or nervous threads, arising from a circle round the mouth ; 
many have four suckers around a prominence, in the form of a proboscis ; 
and, notwithstanding some irregularities, there is always found in the ani- 
mals arranged under this division, traces of a radiated form, indistinctly marked 
in some, but in others, such as the Asteria, the Echini, and the Polypi, stril- 
ingly perceptible. The nervous system in the animals of this division is 
never very evident ; and of acirculation by vessels, asin the previous classes, 
there is no trace. The Holothurie have two vascular appendages, one at- 
tached to the intestines, and corresponding to the organs of respiration, 
and the other serving for the inflation of organs analogous to feet. The 
last of these only appears distinctly in the Echini and the Asterie; in the 
gelatinous substance of the Medus@ are seen tubes more or less complicated, 
connected with the intestinal canal; but none of the appearances are con- 
ceived to have any strong analogy with the circulating vessels of the higher 
animals. Some genera, such as the Holuthuria Echinus, and many intestinal 
worms, have a mouth and anus, with a distinct intestinal canal; others have 
an internal pouch, with only one opening, serving the purposes of a mouth 
and anus; but in the greater number there is only to be discovered a hollow 
cavity in the substance of the body, opening sometimes by many suckers or 
pores. Finally, in the lowest races of the animal kingdom, even this sim- 
ple organization disappears, and nutrition seems to be accomplished by ab- 
sorption, in the manner of vegetables. In regard to their reproduction, sexes 
have been observed in many of the intestinal worms ; others are hermaphro- 
dite and oviparous ; and some seem to be reproduced by gemzne, or buds, ox 
simply by a division of their parts. The conglomerated or compound ar- 
rangement of animals, of which some examples occur among the Mollusca, 
is a common circumstance among the Radiated animals, particularly among 
those named Polypi; and from their aggregation and expansion into trunks 
and branches of various forms, joined to the simplicity of the organization 
in the greater number of the species, originated the term Zoophyta, or ani- 
mal plants. The radiated disposition of their organs, like the petals which 
form the corolla of a flower, seems also to have led to this idea. Indeed, the 
boundary line between the animal and vegetable kingdom seemsat first view 
to be but indistinctly drawn ; and there are objects in both which even accu- 
rate observers are scarcely able to decide, whether they belong to the one or 
the other. In the simplest being, however, the globular form, as Carus ob- 
serves, is the characteristic of animality ; and minute microscopical investi- 
gation detects in the lowest of the animal races a semifluid mass, composed 
of minute globules suspended in slimy fluids while in the organization, the 
cellular texture always predominates. To this characteristic form, the most 
imperfect ani*aated beings add a sensibility to the faintest impressions, tnat 
of light, for example, the power of voluntary motion either in the animal or 
its parts, and the absorption of food into an internal cavity. In the more 
perfect animals, the osseous skeleton serves to cover and protect the centra 
