_Specimens examined._--Total number, 41 (23 males, 14 females, 4 unsexed), as follows: Mariana Islands, USNM--Guam, 20 (May 24, 29, June 6, 8, 14, 15, 16, 18, 23, July 10, 19, 20)--Rota, 2 (Oct. 19, 27)--Saipan, 1 (Sept. 26); AMNH--Guam, 4 (March 7, 9, 20)--Tinian, 1 (Sept. 8)--Asuncion, 4 (Jan. 1, 18, 25); MCZ--Saipan, 3 (Jan. 7, March 20, April 17); Marshall Islands, USNM--Bikini, 6 (Feb. 27, March 2, 16, 19). _Nesting._--_Gygis alba_ does not construct a nest but places its single egg rather precariously in the crotch of a branch in a tree (or on rock). In Micronesia nesting activities have been observed at various times of the year. Yamashina (1932a:409, 410) reported on eggs taken in the Marianas at Saipan on February 2 and in the Marshalls at Arhno on September 26, at Iringlab on October 21 and at Namo on October 19. At Guam a pair of White Terns was seen in a large tree on March 27, 1945, by the NAMRU2 observers. Because of their behavior, it was suspected that they had an egg or young in the tree. Further inspection revealed, on March 31, a downy young sitting in the tree. The young bird was attended by the parents until it began to fly on April 17. Hartert (1898:68) reports that eggs of the White Tern were taken at Saipan on July 28 and August 11. Morrison obtained a male nestling on March 16 and eggs on March 22 at Bikini in 1946. _Remarks._--The White Tern is usually restricted to the remote islands in the Pacific, Indian and South Atlantic oceans; there, according to the latest treatment, which is that of Peters (1934:348, 349), six subspecies are recognized. In studying the geographical variation of the species, the writer has examined 595 adult specimens, including previously unstudied material collected by the Whitney South Sea Expedition, which is deposited in the American Museum of Natural History. This ivory-white species presents an unusual problem in that there are few characters available to distinguish the subspecies. Measurements of taxonomic value include those of the wing, tail, exposed culmen, and depth and the shape of the culmen. There appears to be no significant secondary sexual difference between males and females, and measurements of the two sexes are combined. The chief problem within this species seems to hinge on how to classify isolated, but relatively similar, populations. The examination of the large series of specimens from the Whitney collections has yielded more complete information to assist in the solution of this problem. _Gygis alba alba_ (Sparrman) of the South Atlantic Ocean (Fernando de Noronha, South Trinidad, Ascension, and St. Helena islands) and _G. a. monte_ Mathews of the Indian Ocean (Seychelles, Aldabra, Mascarene and Chagos islands) are isolated populations. Specimens examined are those which have previously been studied by other workers; measurements are shown in table 23.