THE HONEY-GUIDES 23 



tooth found in most birds, althougli the egg-tooth is usually found 

 only on the maxilla and not necessarily at the extreme tip. Rosen- 

 stadt (1902, p. 511; 1912, p. 612) reports that the egg-tooth is formed 

 embryologically on the lower mandible in the domestic chicken as 

 well. Also, Willink (1899) writes that not a few genera of birds 

 have such mandibular, in addition to maxillary, callosities. Among 

 the genera he mentions are Oedicnemus, Haematopus, Numenius, 

 Limosa, Recurvirostra, Sterna, Otis, and Gallinula. The mandibular 

 callosity is generally less elevated and basally broader than the max- 

 illary one.* To this list Stresemann (1928, p. 286) adds that in 

 newly hatched loons (Gavia), hornbills (Bucerotidae) , and some auks 

 (Alcidae) the tip of the mandible, which protrudes beyond that of 

 the maxilla, is hardened into a sharply pointed wedge in the form 

 of an egg-tooth. 



While these records are of interest in demonstrating that the con- 

 dition of mandibular plus maxillary callosities does occur elsewhere 

 in the avian class, these callosities are not extenuated and hooked, 

 but blunt excrescences. Nothing of the sort appears to have been 

 recorded for any other birds, but it may be recalled that in newly 

 hatched woodpeckers, kingfishers, and jacamars the mandible often 

 exceeds the maxilla in length, and the maxilla is often curved down- 

 ward slightly at the tip in some woodpeckers and puff -birds. Coming 

 still closer to the honey-guides in systematic position, in newly 

 hatched prong-billed barbets, Dicrorhynchus jrantzii, Skutch (1944, 

 p. 75) found that "the lower mandibles of their short bills were both 

 longer and broader than the upper mandibles, as in newly hatched 

 woodpeckers, toucans, and kingfishers. Their egg-teeth were less 

 prominent than those of woodpeckers." The Heinroths (1926, p. 321) 

 describe the egg-tooth of the black woodpecker, Dryocopus martins, 

 as a singular, highly peculiar structure on the tip of the maxilla, 

 formed like a peak of an elongated cap on the tip, contrasting sharply 

 in its whiteness from the rosy color of the rest of the bill. No specific 



* Curiously enough, Willink's study appears to have been stimulated by Wein- 

 land's unreliable record (Proc. Essex Inst. (1856-60), vol. 2), p. 115, 1862) of 

 double egg-teeth in Ereunetes pusillus. What bird Weinland had is not clear, 

 but inasmuch as it was collected a few days after hatching at Nahant, Massa- 

 chusetts, it could not have been this sandpiper, which does not breed within 

 many hundreds of miles of that area. 



Figure 4. — a-c, Outline drawing of 2-day old greater honey-guide, X2, showing bill hooks 

 (b), X3, and heel pad (c), X3. d, Longitudinal section of bill of 14-day chick embryo 

 (ex Gardiner), showing egg tooth (e) and oral groove (r). e. Oral groove in a somewhat 

 older chick embryo (es Gardiner). /, Bill of an 18-day chick embryo (ex Gardiner). 

 g, Longitudinal section of bill of Milvus embryo (ex Gardiner), showing mandibular 

 papillum (p). 



