18 
ILLUSTRATED NATURAL HISTORY. 
STAR-FISH : DIVISION KADIATA. 
or of aggregations of similar independent cells ; but in many instances their bodies and organs are 
constructed entirely of a gelatinous cellular matter very like that of which the Protozoa are com- 
posed, and which appears to possess almost an equal power of retaining vitality in its smallest 
particles. As we advance in the group, however, we find the organization of its constituent ani- 
mals growing more and more complicated, from the vital functions becoming more and more 
differentiated — that is to say, performed by organs specially devoted to each ; until, from creatures 
roughly shaped out of a homogeneous semi-gelatinous mass, we gradually arrive at animals fur- 
nished with distinct nervous and vascular systems, with organs of motion and reproduction. 
The most striking character of the animals included in this group consists in the radiate arrange- 
ment of their organs, as in the star-fish, round a central axis, which generally passes through the 
mouth. From this pecuharity they have been denominated by zoologists radiated animals, and 
constitute the division Radiata. This group includes those animals which were formerly supposed 
to approach very closely to plants, or indeed rather to partake of a sort of mixed nature interme- 
diate between animals and vegetables, hence called zoophiles, or animal-plants ; and some authors 
still make use of this name in preference to that of Radiata, to indicate the present group. 
The nervous system can only be recognized distinctly in the most highly organized of these 
animals. In these it partakes of the radiate arrangement of the body, the nerve distributed to 
each division of the body corresponding exactly with those of its neighbor, and arising from a 
separate center. These centers are all placed in a circle round the mouth, and united by a cord 
which forms a complete ring. 
The sense of touch appears to be the only one which can with certainty be ascribed to these 
animals ; this resides in the general covering or integument, and is also frequently exercised by 
special organs. 
All the Radiata possess a mouth and intestinal cavity; but very few of them have a second 
opening for the discharge of fecal matters. They generally possess a more or less distinct vascular 
system : in some of the higher forms a sac-like heart occurs. 
Sexual reproduction occurs in all the Radiata, and the sexes are generally on separate individ- 
uals. Propagation is also very commonly effected in this division by the formation of buds or 
gemmules ; and these either remain attached to the parent stock, which thus goes on increasing 
continually in size, or become free, and lead an independent existence. 
In the two preceding divisions of the animal kingdom we find the body formed upon two very 
