C. E. Beecher — Origin and Significance of Spines. 343 



birds are nearly all that remains of the external fingers, or 

 digits. In the Hoactzin of South America (Opisthocomus 

 cristatus), the young bird has a thumb and index finger, both 

 provided with claws, and climbs about much like a quadruped, 

 using its feet, fingered wings, and beak. According to Lucas, 43 

 a rapid change " takes place in the fore limb during the growth 

 of the bird, by which the hand of the nestling, with its well- 

 developed, well-clawed fingers, becomes the clawless wing of 

 the old bird with its abortive outer finger." Similar claws or 

 spurs occur on a number of other birds, some having functional 

 wings, as in the example just described, and others having only 

 vestiges of wings, as in the Wingless Bird of New Zealand 

 {Apteryx, figure 69). 



66 



67 



68 



TO 



P 



Figure 66. Female of Lernceascus nematoxys. A parasitic Copepod, showing 

 suppression of limbs. Enlarged. (After Claus.) 



Figure 67. Horse-Shoe Crab, Limidv.s polyphemus, showing telson spine and 

 abbreviated abdomen. Reduced. 



Figure 68. A Devonian Phyllocarid, Echinocaris socialis, showing spiniform 

 telson and cercopods. 



Figure 69. Wing of Apteryx australis. x |. (After Romanes.) 



Figure 70. Skeleton of right fore limb of the Jurassic Dinosaur, Igicanodon 

 bernissartensis, showing suppressed first digit, x ¥ ^. (After Dollo. 16 ) 



Another example may be taken from the Dinosaurian Kep- 

 tiles. The Jurassic genus Iguanodon, from England and 

 Belgium, belongs to a group (Ornithopoda) in which the num- 

 ber of functional digits varies from three to five in the manus, 

 and from three to four in the hind feet. In this genus, the 

 hind foot had three functional toes, representing the second, 

 third, and fourth of a normal pentadactyl foot. The first is 

 represented by a slender tarsal bone alone, while the fifth is 

 completely suppressed. The manus, or fore foot, of this ani- 



