Specimens (12): [Male], 40812, testis 10 × 4 mm., 17.1 gm., molting--1st, 2nd, and 3rd primaries ensheathed (July 17), and [Male], 40813, testis 7 × 4 mm., 18.2 gm. (July 17), 1 km. N, 13 km. W Escárcega; [Female], 40803, ovary 9 × 5 mm., ova to 1 mm., brood patch (July 21), [Male], 40805, testis 11 × 6 mm., 18.5 gm. (July 21), [Male], 40804, 18 gm. (July 21), and [Female], 40802, ovary slightly enlarged, molting--2nd and 3rd primaries ensheathed (July 21), all from Pisté; [Male], 40806, 17.5 gm., molting--1st primaries ensheathed (July 21), 6-1/2 km. W Pisté; [Female], 40808, ovary 5 × 3 mm., 17.4 gm. (July 28), [Male], 40807, testis 5 × 3 mm., 17.7 gm., molting--3rd and 4th primaries ensheathed (July 28), [Male], 40809, testis 2 × 1 mm., 17.5 gm. (July 29), and [Male], 40810, testis 3 × 2 mm., 18.7 gm., molting--1st, 2nd, 3rd, and 4th primaries ensheathed (July 30), from Pueblo Nuevo X-can; [Male], 40811, testis 3 × 1 mm., 18.7 gm., molting--4th, 5th, and 6th primaries and middle pair of rectrices ensheathed (August 14), 4 km. NNE Felipe Carrillo Puerto. Mallophaga: _Philopterus_ sp. July 21. _Vireo magister_ (Lawrence): Yucatán Vireo.--Breeding on the peninsula has not been recorded previously. A male, beginning to molt, taken on August 10 on Isla Cozumel had enlarged testes, which were apparently regressing. Specimens (3): [Female], 40814, ovary inactive, 17.7 gm. (August 2), Isla Mujeres; sex? 40815, 19.5 gm. (August 9), and [Male], 40816, testis 6 × 3 mm., 20.2 gm., molting--1st, 2nd, and 3rd primaries ensheathed (August 10), 3-1/2 km. N San Miguel, Isla Cozumel. _Cyanerpes cyaneus carneipes_ (Sclater): Blue Honeycreeper.--Paynter (1955a:283) collected specimens that were breeding in April. Testes were fully enlarged in two August-taken specimens and courtship rituals were observed in two pairs seen on August 3 at Puerto Juarez. Specimens (3): [Male], 40817, 15.5 gm. (July 21), 6-1/2 km. W Pisté; [Male], 40818, testis 12 × 6 mm., 12.1 gm. (August 3), 4 km. WSW Puerto Juarez; [Male], 40819, testis 8 × 6 mm., 11.6 gm. (August 14), 4 km. NNE Felipe Carrillo Puerto. _Coereba flaveola caboti_ (Ridgway): Bananaquit.--Specimen (1): [Female], 40820, ovary inactive, 5 × 3 mm., 11.0 gm., molting--1st and 2nd primaries ensheathed, 3rd and 4th primaries missing (August 10), 3-1/2 km. N San Miguel, Isla Cozumel. _Dendroica petechia rufivertex_ (Ridgway): Yellow (Golden) Warbler. --Specimens (5): [Female], 40831, ovary inactive, 8.0 gm. (August 8), sex?, 40832, imm. (fresh, first winter plumage), 10 gm. (August 8), [Female], 40830, ovary inactive, 10.0 gm., molting--4th and 5th primaries ensheathed (August 9), [Female], 40833, ovary inactive, 8.5 gm. (August 9), and [Female], 40834, ovary inactive, 7.8 gm. (August 10), all from 3-1/2-4 km. N San Miguel, Isla Cozumel.