804 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 prohoscis ; 

 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, hut in others, such as the Asterice, the Echini, and the Polypi, strik- 

 ingly perceptible. The nervous system in the animals of this division is 

 never very evident ; and of a circulation by vessels, as in the previous classes, 

 there is no trace- The Holothuria 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 Asterice; in the 

 gelatinous substance of the Medusa 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 gemma:, or buds, or 

 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 Avhich 

 form the corolla of a flower, seems also to have led to this idea. Indeed, the 

 boundary line between the animal and vegetable kingdom seems at first view 

 to be but indistinctly drawn ; and there are objects in both which sven 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 Cams 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 animated beings add a sensibility to the faintest impressions, that 

 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 



