Glass 2. Anthozoa. Order 2. Zoantharia. 



117 



Pig.71. Portion of an arbor- 

 escent Madreporarian, 

 which increases by budding. — 

 After L. Agassiz. 



the sides of which the 

 this arrangement, the 



gastric cavities are connected by a system of fine canals. The 

 outer form of the colony corresponds with that of the skeleton, 

 and is very varied. Some forms are 

 arborescent, others massive, the individuals 

 situated close together like the cells of 

 honeycomb ; the upper portions into which 

 the skeleton does not extend are for the 

 most part independent, whilst the portions 

 surrounded by the skeleton are fused 

 with the neighbouring individuals, either 

 throughout their whole length or in the 

 lower region only. Sometimes, but this 

 is only exceptionally the case, the con- 

 nection between adjacent polyps is still 

 more intimate ; the oral openings are 

 indeed separated, but the gastric cavities 

 communicate freely, and in the dry skeleton, 

 each individual is not, as in other cases, 

 indicated by a star separated from others 

 by its thecaj but a whole row of in- 

 dividuals is indicated by a groove, from 

 septa project : in correspondence with 

 tentacles are not situated in circles round 

 the mouths, but in a double row along the 

 groove (Fig. 72). 



Only in somewhat rare instances, do the new in- 

 dividuals, formed by budding or fission, separate 

 o ff from the parent. This happens, for instance, 

 in the Actinia without skeletons, in which budding 

 as well as fission, both transverse and longitudinal, 

 may occur. In some forms with a calcareous 

 skeleton, the buds or individuals f omied by fission 

 may, in rare cases, separate, taking with them a 

 portion of the calcai-eous skeleton. The Mush- 

 room Coral (Fungia), a solitary form, which 

 lies freely on the bottom of the sea, and attains 

 a considerable size, develops in this way by 



the transverse fission of a small attached solitary coral (or fi'om a colony 

 consisting of qviite a few individuals). After fission, the individuals separate 

 and undergo fm-ther growth. 



Coral reefs, which are so frequently met with in the seas of 

 the Torrid Zone, and which may be even miles in length, owe their 

 origin chiefly to different calcareous Zoantharia. Besides these, 

 certain other animals, notably certain Hydroids [Millepwa, 

 p. 106) also assist in the formation of the reef. The reef con.sists 

 in part of skeletons of dead colonies, in part of living colonies, which 

 have attached themselves to the latter. Upon and within the reef 

 there live a great number of other animals, which are to some extent 



Fig. 72. Small portion of the 

 surface of a Coral in which the 

 individuals are incompletely 

 separated (HeliastrcBa). Three 

 oral apertures may be noticed ; 

 tentacles in two rows. — After 

 M. Edwards and Haime. 



