30 Transactions. 



While it is iully understood that the observation of the visible zoological 

 and geological facts of the present may absorb a large share of the atten- 

 tion of a reef-investigator, it is urged that he should frequently, while still 

 in the field, take enough time from observational work to think out as 

 carefully as possible the invisible conditions of the past according to each 

 and every theory known to him, and that having done so he should return 

 to an examination of the visible facts in order to discover which one of 

 his theories they best support. New Zealand is favourably situated as a 

 starting-point for the study of coral reefs ; hence the scientific world must 

 look to New Zealand students for new light on this old problem. 



Eeferences. 



Daly, R. A., 1910. Pleistocene Glaciation and the Coral-reef Problem, Amer. Journ. 

 Scl, vol. 30, pp. 297-308. 



1915. The Glacial -control Theory of Coral Reefs, Proc. Amer. Acad. Sci., vol. 51, 



pp. 157-251. 

 Davis, W. M., 1913. Dana's Confirmation of Darwin's Theory of Coral Reefs, Amer. 



Journ. Sci., vol. 35, pp. 173-88. 

 — — 1914. The Home Study of Coral Reefs, Bull. Amer. Geog. Soc, vol. 46, pp. 561-77, 



641-54, 721-39. [The omission of the name of E. C. Andrews on p. 724 



(eleventh line from bottom) of this article, which was printed during my 



absence on the Pacific, is a regretted oversight.] 



1915. A Shaler Memorial Study of Coral Reefs, Amer. Journ. Sci., vol. 40, 



pp. 223-71. 



191Ga. Problems associated with the Origin of Coral Reefs, Sci. Monthly, vol. 2, 



pp. 313-33, 479-501, 557-72. 



1916b. Clift Islands in the Coral Seas, Proc. Nat. Acad. Sci., vol. 2, pp. 283-88. 



1916c. Extinguished and Resurgent Coral Reefs, Proc. Nat. Acad. Sci., vol. 2, 



pp. 466-71. 



1916d. The Origin of certain Fiji Atolls, Proc. Nat. Acad. Sci., vol. 2, pp. 471-75. 



1917a. The Great Barrier Reef of Australia, Amer. Journ. Sci., vol. 44, pp. 339-50. 



1917b. The Isostatic Subsidence of Volcanic Islands, Proc. Nat. Acad. Sci., vol. 3, 



pp. 649-54. 

 ■ — — 1918. The Subsidence of Reef-encircled Islands, Bull. Geol. Soc. Amer., vol. 29, 



pp. 489-574. 

 Skeats, E. W., 1918. The Coral-reef Problem and the Evidence of the Funafuti 



Borings, Amer. Journ. Sci., vol. 45, pp. 81-90; The Formation of Dolomite and 



its Bearing on the Coral-reef Problem, ibid., pp. 185-200. 



Art. III. — On the Occurrence of Two Unusual Blood-vessels in 



Hyla aurea. 



By Professor W. B. Benham, D.Sc, F.R.S., Button Memorial Medallist. 



{Read before the Otago Institute, 9th July, WIS ; received by Editor, 17th December, 



WIS ; issued separately, 14th May, 7979.] 



In former days, when fixity of species was a tenet of biologists, any imusual 

 occurrence in the anatomy of animals was spoken of as an " abnormality " ; 

 but nowadays biologists are familiar with the fact that no two individuals 

 of a given species are absolutely identical in all their parts — every organ, 

 both external and internal, may present some more or less profoimd differ- 

 ence when compared with other individuals, and these difierences are known 

 as " variations." In the blood-system, for example, although the main 



