404 



As sand is deposited in the lagoon it tends to obliterate the coral 

 growth, and so a lagoon, that at first tended to become shallow by the 

 upgrowth coral colonies, ultimately becomes devoid of living coral, and 

 to shoal entirely by the deposition of sediment. In the Cocos-Keeling 

 atoll, the history since 1825 shows a steady filling-in of the lagoon. 

 The continuation of the process that formed the perfect atoll, therefore, 

 tends to obliterate the lagoon. The lagoon shores gain on the lagoon 

 water, and banks rise up in its shallower parts; the windward side of 

 the lagoon, if it be of large size, being the first portion to become 

 obliterated. 



The explanation of the origin of fringing reefs follows the same 

 lines. On any platform that lies above the limiting line of sedimen- 

 tation, reef-corals mùU develop, when the conditions of the water are 

 suitable. Fringing reefs are merely reefs taking origin upon the sub- 

 marine slopes of oceanic land, when these slopes afford a foothold in the 

 wave-stirred area. 



Barrier-reefs were explained in 1856 by Prof. Le Conte as being 

 fringing reefs of which the growth was "limited on one side by the 

 muddines of the water, and on the other by the depth." In 1884 

 Dr. Guppy independently furnished the same explanation. This ex- 

 planation, which is an isolated and discordant thing when "Subsidence" 

 or "Solution" is taken as accounting for atoll formation, becomes of 

 consequence, and falls into line with other ascertained facts, when the 

 importance of "Sedimentation" is appreciated. (For permission of re- 

 publishing certain parts of this article I am indebted to the Zoological 

 Society of London.) 



8. Über die sogenannte metaniere Segmentierung des 

 Appendicularienschwanzes. 



Von J. E. "W. Ih le, Zoolog. Institut Amsterdam. 



eingeg. 8. Dezember 1909. 



Zu Anfang dieses Jahres erschien eine schöne Abhandlung von 

 E. Martini über »die Konstanz histologischer Elemente« (Zeitschr. f. 

 wiss. Zool. Bd. XCTI), worin er einen sehr wichtigen Beitrag zur Kennt- 

 nis der Anatomie und Histologie von OiixVpIeura longicauda liefert. In 

 dieser Schrift untersucht er auch ausführlich den Bau des Schwanzes 

 und kommt (S. 611) in bezug auf die Segmentierung zu dem Ergebnis, 

 daß, »wenn man selbst bei Appendicularien eine Segmentierung fände, sie 

 doch so verschieden von der des Äniphioxiis sein würde, daß es zweifel- 

 haft wäre, ob man sie mit der Segmentierung der Yertebraten in phylo- 

 genetischen Zusammenhang bringen könnte«. 



Auf der 19. Jahresversammlung 1909 der Deutschen Zoologischen 



