EXPLANATION OF PLATE X. 



Fig. 1. Section cutting longitudinally and vertically through the basal part of the 

 Wolffian ridge of the chick, six days old; n, medulla spinalis; shl, hinder 

 somites, which are drawn togetb'^r more or less at their ventral end, where 

 they are destined to furnish the muscular and nervous supply of the hind 

 limb ; st, thoracic somites ; hi, hind limb ; fl, fore limb, x 16. 



Fig. 2. Longitudinal nearly vertical section through the base of the dorsal fm of 

 an embryo of Squaius a little off of the median line, to show the muscular 

 bud3 7>i&wi&, which are thrust upward into the dorsal fin-fold, and from 

 which the muscnlpr apparatus of the fin is derived; ep, epiblast; c, con- 

 nective tissue. X 35. 



Fig. 3. Transverse section through the pectoral tin of a young embryo of Scyllium 

 siellare, from Balfour ; v v, vessels ; mpt, basipterygial bar (metapterygium) • 

 m, muscles ; cr, cartilaginous rays ; mes, mesoblast ; hf, horny fibers be- 

 tween mesoblast and epiblast. 



Fig. 4. Pelvic fin of a very young female embryo of Scyllium stellare; bb, basiptery- 

 gium ; pu, pubic process of pelvic girdle ; il, iliac process of pelvic girdle ; 

 /, foramen through pelvic plate ; hf, horny fibers. From Balfour. 



Fig. 5. Transverse section through the pectoral fin of a recently hatched salmon ; 

 vv, vessels; be, pericardiac cavity; ao, aorta : dc, ductus Cuvieri ; del, 

 merabrauous matrix of clavicle; bp, basipterygial or cartilaginous pec- 

 toral plate ; mes and c, mesoblast or connective tissue ; my, myotomes ; hf, 

 horny fibers ; m, muscles of pectoral inserted into the edge of the pectoral 

 plate ; ep, epiblast. 



Fig. 6. A nearly median section through the dorsal of Amiurua, fifteen days old^ is' 

 is', basilar intemeural or median actinophoral cartilages ; ii, interneurals; 

 r r, membranous matrix of permanent rays, the last one, r', showing the 

 effects of concresence at its lower end ; c, connective tissue ; ea', supra- 

 carinal muscle ; es, erectores, and ds, depressores spinas muscles ; 7)iy, myo- 

 tomes. X 35. 



Fig. 7. Transverse section through the central part of the tail of the shad (Aloaa), 

 cutting the chorda, ch, and medulla spinalis, n; ep, epiblast; mea, meso- 

 blast, with the horny layer hi between them, x "6. 



Fig. la. A portion of the horny layer M of the preceding nearly opposite the 

 chorda, which shows itself differentiated into embryonic rays or fibers 

 hf. X 600. 



Fig. 8. Pectoral fin of a young embryo of Scyllium in longitudinal and horizontal 

 section ; pc, wall of peritoneal cavity ; /, foramen in the pectoral girdle ; 

 pg, pectoral girdle in transverse section ; cr, cartilaginous rays ; hf, horny 

 fibers or rays. 



Fig. 9. Horizontal longitudinal section through the pectoral of an embryo of Squalua 

 to show some of the muscular buds, wife, which have been thrust out by 

 the post-branchial somites into the jiectoral fold ; cr cr, rudiments of car- 

 tilaginous rays ; v v, vessels ; my, my myotomes, x 35. 



Fig. 10. Transverse section ti 70ugh the ventral fin-fold of a recently-hatched shad 

 embryo in front ol the anus ; i, intestinal lumen ; mes, mesoblast ; ep, epi- 

 blast or larval skin ; h, homogeneous matter which fills the fin-fold before 

 the embryonic rays are differentiated, x 96. 



124 11(34 



