GENERAL CHARACTERS OF RADIATA. 



43 



calcareous matter either in the centre of each fleshy column, so as to form a 

 solid stem, or on its exterior, so as to form a tube. In other cases it is horny ; 

 and then it may be a flexible axis, or a delicate tube. Both the stony and 

 horny Corals frequently possess the form of plants or trees: and as their 

 skeletons are often found with no obvious traces of the animals to which they 

 belonged, they have been accounted Vegetable growths. There is not the 

 least doubt, however, as to the Animal origin of the greater part of these plant- 

 like structures. 



7. The affinity between the lowest Radiata and Plants, in regard to the 

 vital phenomena they exhibit, is still more close than that manifested by their 

 structure. Although, in the higher, groups, movements may be constantly 

 witnessed, which evidently indicate consciousness and voluntary power, this 

 is far from being the case in the lower. There are many tribes, whose recep- 

 tion of food, growth, and reproduction, are not known to be accompanied by 

 any phenomena which distinctly indicate their animal character. The most 

 violent lacerations produce no signs of sensibility ; and the movements occa- 

 sionally exhibited by them have not so much of a spontaneous aspect as 

 those which are performed by many plants. This is the case, for example, 

 with the Sponge tribe; and also with a number of microscopic species. So 



Fig. 1. 



Asterias auraniiaca, with the upper side of the hard envelope removed ; a, central stomach; b, coeca 

 upon its upper surface, probably answering to the liver ; c, c, coecal prolongations of stomach into rays; 

 c', c', the same empty ; d, the same opened ; e, under surface, showing vesicles of feet ;/", vesicles con- 

 tracted : showing skeleton between them. 



