G36 



RADIATA. 







VARIOUS RADIATE ANIMALS UPON THE SEA SHORE. 



tlic only aperture of the digestive cavity, and is quite destitute oi any masticating apparatus. Tlie 

 skin in the compound polypi, ■which are able to retract themselves into firm cells or tubes, is 

 exceedingly soft and tender ; but in the solitary species it frequently acquires a leathery consist- 

 ence, forming a closed sac, within which the more delicate tentacles can be retracted at pleasure. 

 In many cases the skin contains urticating organs, consisting of minute transparent vesicles, from 

 which long spiral threads and a caustic fluid are emitted, which cause a stinging sensation on 

 coining in contact with the human skin. Reproduction takes place in these animals both by 

 means of ova and by germination or budding. The sexes are always united in the same indi- 

 vidual. This class is divided into three orders — Helianthoida, Asteroida, and Hydroida. 



Before we proceed, however, to notice these separate divisions, we must more fully apprise the 

 reader of the peculiar nature of some of the animals belonging to this order. It is to be borne 

 in mind, that — as we have stated — some polypes are simple and others are congregated — these 

 latter being united into one living whole, while, at the same time, each acts for itself; one con- 

 tracting, another expanding at the same instant. In one sense we may consider each polype as 

 a distinct being; in another sense, as forming a part of a compound unity through which vitaUty 

 is equally diffused. In these aggregated forms the polypes all labor to one end ; they constitute a 

 community, every individual of which contributes to the nutrition of the general body. But as 

 there are no nerves, they can neither participate in each other's movements or each other's feelings. 

 If one polype is destroyed, the rest are unaffected. We may commence our observations by remark- 

 ing, that all ideas of life derived from a consideration of the higher animals of creation must here 

 be banished. Deadness to pain, yet feeling for light, contractility, expansibility, and motion with- 

 out muscles ; digestion and nutrition without lacteals, absorbents, or blood-vessels ; reproduction 

 by simple division or bud-like sprouts ; the vital unity of myriads, and yet their personal distinct- 

 ness — these are the curious, strange, anomalous characteristics which belong to the animals we are 

 now about to contemplate. 



