MOEPHOLOGT OF THE GALLIXACE.^. 233 



variety — a variety that gives iis a monstrosity that is most certainly not a " new thing," 

 but an atavistic relapse, and which is very constantly hereditary, — we have the 1st toe 

 {dg}) showing the two modes of increase of the rays of an ichthyopterygiiim, or 

 fish-fin. Here the increase in number takes place as in the Elasmobranchs ; an 

 additional ray is added on the inside, and the normal first ray increases, as the rays of 

 the Skate's huge pectoral fin increase, namely by a single phalanx having a pair of 

 phalanges on its distal end. 



Here Morphology and Teratology meet. In perfectly normal Eowls there is an 

 additional element of the limb on the tibial side, namely the spur, so common in the 

 phasianine Fowls, and in one kind is repeated, Pohjplectron having two spurs. 



The Ornithologists who treat only of adult birds in their memoirs, tell us with the 

 utmost confidence that these parts have nothing \^^liatever to do with the normal ele- 

 ments of the foot, and have nothing in common with normal claws or ungual phalanges. 

 A single glance at the fore foot of the Bernissart Iguanodon (Dollo, Bull. Mus. Roy. 

 Hist. Nat. Belg. t. ii. pi. v.) would have cast a doubt upon this confident opinion of 

 Mr. J. Amory Jeffries (Proc. Boston Soc. Nat. Hist. 1881, vol. xxi. p. 301) and Dr. P. L. 

 Sclater (see Ibis, vol. iv. 1886, 5th series, i^p. 117-151 and pp. 300, 301). Everywhere 

 marginal remnants of mesopodial, metapodial, and phalangeal elements are being dis- 

 covered in the limbs of Amphibia, Reptilia, Aves, and Mammalia ; the cheiroptery- 

 gium is merely what it is by " natural selection," and the " old things " are not always 

 done away in the making of this new and more perfect form of limb. 



At this 3rd stage, just below the middle of the 2nd metatarsal, on its inner side, 

 one of the scales of the shank is circular ; within that circular scale there is a lenticular 

 mass of fibro-cartilage (Plate XXIV. fig. 4, spr.) ; that mass is to me a remnant of a " pre- 

 hallux ;" we shall see how this part behaves in the further stages. 



In the 4th stage (Plate XXIV. fig. 6), a little after the middle of incubation, the 

 independence of the intermedium {i.) is further shown by an ectosteal cap on its shiainken 

 upper or proximal end. Its broad distal part is not wholly fused with the region of the 

 fibulare (fbe.), and its inner angle is continuous with the top of the region of the tibiale ; on 

 its tibial side a new band of cartilage is formed ; this is the tendon-bridge, and is an 

 addition to the tibia. The true tarsals, or mesopodials, are wholly unossified at this 

 stage after 12 days' incubation; but the true proximal nuclei arc quite fused together, 

 and form the well-made double condyle, which rolls in the connate distal tarsals (df.). 

 The lower end of the fast-ossifying tibia (t.) is still distinct from the proximal tarsal 

 mass, and the distal tarsal mass is still quite distinct from the closely-packed metatarsals. 

 Not only so ; that connate mass has grown down behind the tops of the approximate 

 rods ; the fan-shaped outgrowth, Avith its ridges and grooves, clamps them together. 

 In its normal place, between and behind the astragalus and the region of the 

 middle cuneiform, we see the scaphoid, or centrale, as a thick, solid, subcrescentic 

 wedge of true,or hyaline, cartilage. 



In the 5th stage, or Chicks from eggs that have been sat upon for 14 or 15 days 

 (Plate XXIV. figs. 8, 9), the metamorphosis of the elements of the leg is far advanced, 

 and yet they are largely distinguishable. The proximal end of the tibio-tarsal region is 



