Introduction to Animal Morphology. 1 1 r 



tons, which may be (a) isolated, or amalgamated with a horny* 

 or chalky interstitial substance (axis of Melithaea, &c.), 

 •or (/3) lamellated, with or without an organic basis (as 

 Gorgonia or Primnoa), or (y) crystalline, increasing by 

 chalky deposits, with scarcely an organic basis (Madrepores). 

 Spicules (Sclerodermites) are fusiform, laminar, ovoid, or 

 stellate ; a spicular skeleton is 2. polypieroid ; one continuously 

 calcified, a polyparium or coralliim ;\ the hard tissue is 

 Sclerenchyma, which may be compact or porous. Each 

 persona (Corallite) of a polyparium consists of some of the 

 following parts : — i. A calcified, ab-oral foot, continued in 

 colonial forms into the coenenchyma. 2. The calcified 

 •enderon of the persona {Jhecd) forming the wall of the cup 

 •{calyx) ; this may consist of two layers, an endo- and an exo- 

 theca. 3. Calcified mesenteries {septaX), passing in from the 

 ■endotheca, dividing the calyx longitudinally into radially- 

 arranged loculi. 4. Rib-like ridges on the outside of the 

 cxotheca, opposite each system or between two {costae). 

 5. Outside the exotheca, an ecderonic investing layer or 

 ■ipitheca may form, often developed in inverse ratio to the 

 thickness of the theca. 6. Between the simple zooids of a 



* Apparently homy, but really chitinoid ; intermediate between Chitin 

 and Keratin. 



t Analysis of Coral gives 89—96 per cent, of Calcium Carbonate ; 

 •O'3-250 of Calcium and Magnesium Phosphate and Fluoride ; 0-50 organic 

 basis ^vith traces of Silica, Iron, Alumina. Magnesium Floride is present 

 in Pcecilopora. There is, however, much variety. Silica may in some 

 •cases reach 25 per cent. ; Magnesia, 45 per cent. The specific gravity of 

 Coral averages from 2-20— 2-80. 



X Septa grows in cycles, the five or six primary folds form the first, the 

 secondary the second (also of five or six). Between these a third cycle 

 forms, of twelve laminae, one in each interval. The fourth cycle consists of 

 two orders of septa, one between every first and third, and one of still 

 ■shorter plates between the second and third. The fifth cycle consists of 

 three orders : one of shorter plates than the fifth order, between those of 

 the first and fourth ; a seventh order between the second and fifth ; an eighth 

 between the third and fourth, &c. Each order after the third cycle consists 

 of twelve laminae ; so when a whorl consists of eight orders they will follow 

 each other thus : — i, 6, 4, 3, 8, 5, 7, 2, 7, 5, 8, 3, 4, 6, I, &c. 



