TRANSACTIONS OF SECTION D. 685 



Decalcification of the coral stoclis has revealed the general occurrence of boring 

 filamentons aUjcc of both green and red species. Their corrosive activity was shown 

 to result in the ultimate destruction of coral masses, and has an important bearing 

 upon theories of the disappearance of coral roclf. The colours of West Indian 

 living polyps are mainly due to the presence within the endoderm of symbiotic 

 yellow cells — zoo.ratithellee : this colour may be modified by pigment cells, accumu- 

 lations of pigment granules, or superficial deposits. 



The column-wail never exhibits more than a feeble diffuse endodermal sphincter 

 muscle, and in most species the wall can overfold the tentacles and disc. The 

 tentacles are mostly knobbed and in close alternating hexameral cycles, but in 

 some forms they are widely apart. The stomodccum is without true siphonoglyphs 

 or gonidial grooves; in some the walls are deeply ridged and grooved all round. 

 The mesenteries in genera reproducing by budding conform to the cyclic hexameral 

 plan, while this is altogether departed from in forms increasing by fission. The 

 mesenterial Jilaments are simple, never trilobed as in most Actinians ; they can be 

 extruded through any part of tiie polypal wall along with the mesentery to which 

 they are attached. The skeleton or corallum is an ectoplastic formation laid down 

 within a mesogloea-lilie matrix. 



Asexual reproduction is by gemmation and fissiparity. In gemmation each new 

 polyp reproduces all the essential features of the larval polyp ; in fission no new 

 individuals are produced, the original polyp merely becomes more and more com- 

 plex and multioral. The enlarged polyps sometimes met with in a state of fission 

 on gemmiferous colonies are shown to represent a specialised form of reproduction 

 termed Jissijjarous gemmation. 



Coral polyps are hermaphrodite, but protogyny and protandry seem to occur. 

 The narrow aboral pole of the larva is usually provided with a special nervous 

 development which seems to represent a larval sense organ. The primary six pairs 

 of mesenteries {protocneines) arise as bilateral pairs in a succession which is ap- 

 parently the same in all species ; the six pairs constituting the secondary cycle 

 arise bilaterally as unilateral pairs in a dorso-ventral sequence ; the twelve pairs 

 forming the tertiary cycle also appear as unilateral pairs in a bilateral manner 

 from the dorsal to the ventral aspect, but in a two-fold succession. 



The studies so far conducted on the Tetracoralla or Hiigosa indicate that the 

 primary septal plan is hexameral. The metasepta appear as successive bilateral 

 pairs from a single region within only four of the six exoccBlic chambers, the corallite 

 retaining in the adult a bilateral symmetry, not the multicyclic radial condition. 

 The septal development is such as would be followed in polyps with a mesenterial 

 growth similar to that in recent Zoanthids, except that here additional mesenterie.s 

 arise within only the two ventral exoccelic chambers. 



2. The Coral Formations of Zanzibar and East Africa. 

 By Cyril Crossland. 



Although the land fauna of Zanzibar and East Africa is already well known, 

 very little attention had been paid to that of the sea until Sir Charles 

 Eliot, Iv.O.M.G., was appointed II. M. Consul-General at Zanzibar, and Commis- 

 sioner for British East Africa, when he generously provided for the author to 

 accompany him. 



The island of Zanzibar is 60 miles in length by 20 in breadth. The outline 

 of the east coast is very regular, its only prominent features being an outlying 

 reef, called Mnemba, in the north, and Chuaka Bay at about the middle 

 of its length. The whole extreme part of the island is composed of coral lime- 

 stone or ' rag,' low and deeply undermined cliffs which form the greater part of the 

 east coast and of Pemba .and the mainland. Below these is a very regular fringing 

 reef from 1 to 3 miles wide, upon the edge of which the surf breaks, leaving 

 a sheltered boat channel along the shore. Beyond the edge of the reef the depth of 

 the water drops almost at once 10 or more fathoms. The larger features of the 

 reef are descriDed in previous accounts as being of the usual kind, and due to the 



