116 



Goelentera. 



animal (as in Fig. 69 A), so as to form a cylindi-ioal calcareous deposit 

 external to the body- wall (and of com-se external to the theca) ; this is the 

 epitheca. The skeleton is thus a purely external, cuticular 

 strxicture, secreted hy the ectodemi. 



Fig. 69. A diagrammatic longitudinal section of a Madrei orarian which has only just 

 attached itself, passing between two septa. B transverse section of the lower end of the 

 same. For the sake of simplicity, only 6 septa and 6 mesenteries are drawn, instead of 12. 

 i eiidoderm, m internal mouth, m' external mouth, mi mesogleea, sk mesentery ; st septum, 

 t tentacle, y ectoderm. The skeleton is drawn black.— Orig. 



Between the septa in the lower portion of the animal, small, calcareous 

 transverse beams or platforms often develop, passing from one septum to another 

 (synapticulse). In the lower region, the septa often fuse in the middle, and 

 from the point of fusion there usually arises one or more vertical columellae. 

 All the septa are not equally well- developed ; those last formed do not reach so^ 

 far in as the older ones, with which they alternate regularly. In proportion as the 

 animal grows in height, the lower portions of the septa and the theca thicken so 

 that the lower pai-t of the skeleton becomes more solid and compact than the 

 upper. In older animals the soft parts withdraw from the lower portions, 

 leaving this region of the skeleton naked. 



The majority of Zoantharia, 

 especially those which are fur- 

 nished with a skeleton, form 

 colonies by budding or by 

 longitudinal fission ; the colonies 

 usually consist of a great num- 

 ber of individuals. In budding, 

 a lateral evagination arises from 

 the body-wall and gradually 

 develops into a new individual ; 

 longitudinal fission occurs by 

 the formation of a new mouth 

 on the oral disc, the latter 

 becoming oval, and finally divid- 

 ing to form two {see Fig. 70), 

 whilst a corresponding division 

 of the whole animal occurs. 

 Just as in the Alcyonaria, the 





<riw:'^ 





Fig. 70. Portion ofamassive Madre- 

 p o r a r i a n ; two individuals (one on the right 

 above, one centrally) in tlie act of dividing 

 longitudinally. — After Dana. 



