2 ARKIV FÖR ZOOLOGI. BAND 11. N:0. 12. 



A similar structure has also been found on the foot of 

 the young of a Blue-throated Barbet {Cyanops asiatica Lath.) 

 as recorded by Pycraft (Bull. Brit. Ornith. Club. vol. 8, 

 p. XL, 1899), in the Common Green Woodpecker {Picus vi- 

 ridis viridis Linn.) as shown by Stonham (Ibis 1909, p. 612) 

 and then lately by Seth Smith in Selenidera maculirostris 

 LiCHT. (Proc. Zool. Soc. London 1913, p. 1095—1096). 



In order to ascertain whether tbese curious organs reallv 

 are used for locomotion, it would be of interest to find out 

 whether other species of birds nesting in holes in trees, or 

 in excavated holes in the ground possess a similar structure. 

 I have therefore looked through the material in the R. Nat. 

 Hist. Museum of Stockholm and have come to the following 

 conclusions. Almost all species of birds nesting in hollows 

 are in possession of more or less well-developed pads covering 

 the metatarsal joints. These pads are, however, mostly quite 

 smooth, though easily defined by means of their thickness. 

 They are generally covered with more or less irregular scales 

 which mostly are larger than those of the surrounding parts 

 of the tarsi. Only in a few families viz. the Rhamphastidce, 

 the Capitonid(B and the Picidce they are furnished with pointed 

 tubercles, but in some other families such as the Coraciidce, 

 the Irrisoridce, and the Meropidce the edges of the scuta are 

 slightly raised above the level of the middle parts and then 

 form a fairly rough surface by means, of which the young 

 birds are able of pushing themselves forwards. In the first- 

 mentioned three families the pointed tubercles are not being 

 shed un til a long time af ter the bird has left the nest, as 

 shown by several specimens in our collections. 



As is known the Birds are only extremely modified Rep- 

 tiles. The ancestors of the Birds have most probably been 

 covered by horny scales, similar to those found among these 

 animals. The more the Birds have been modified to their 

 present state of development the more these scales have 

 been löst. However, traces of the Reptile scales may still 

 be observed, for instance on the horny covering of the tarsi 

 and that of the bill. The scales of several reptiles are show- 

 ing a similar structure to those found on the heel-pads of 

 several birds as for instance those of the soles of the feet 

 in several Agamidce which possess some conical tubercles which 



