6 THE SUB-KINGDOM COELENTERATA. 



of a^a\7](j)rj, a term understood by some modern 

 naturalists in a more restneted signification. 



A few of the Coelenterata are microscopic, but 

 by far the majority are of appreciable size, and 

 some attain considerable dimensions. Multiplica- 

 tion by gemmation is of common occurrence among 

 the members of this sub-kingdom, and when, as 

 frequently happens, the growths thus formed re- 

 main permanently in connection with the organ- 

 ism from which they originally sprouted, it is 

 evident that this process, repeated several times, 

 may give rise to aggregate masses, the limits of 

 which it is not possible to define. In form the 

 Coelenterata vary considerably, presenting, in many 

 cases, an external resemblance, sufficiently re- 

 markable, to certain members of the vegetable 

 kingdom. 



The Coelenterata possess no proper blooa-vascu- 

 lar apparatus, distinct from the somatic cavity or 

 its processes. The cilia which line the endoderm 

 promote by their motion the circulation of the 

 nutritive, or somatic, fluid occupying the general 

 cavity of the body, and, in like manner, respiration 

 is effected by the cilia of the ectoderm. Both of 

 these ciliary movements are assisted by the con- 

 tractions of the body walls, mthin which muscular 

 fibres may, not unfrequently, be observed. In- 

 dications of a nervous system and organs of sense 

 have been met with only in a few instances. Other 

 structures, whose function would seem to be se- 

 cretive, are not, however, wanting. Most of the 

 Cmlenterata are provided with prehensile append- 

 ages, or ' tentacula,' and, in many of these animals, 

 special organs, adapted for locomotion, are super- 



