PROCEEDINGS OP UNITED STATES NATIONAL MUSEUM. [1885. 



EXPLANATION OF PLATE IX. 



Eefbeences : a, anal flu ; ab', branchial artery ; &, basioranial end of chorda ; bh, branchial arch ; c, 

 cartilaginous axis of branchial filament ; ch, chorda dorsaUs ; e, end organs or nenromasts 

 on the cheeks ; hs, haemal cartilages ; I, intervertebral ligaments ; ins, medulla spinalis ; 

 n, nerves to neuromasts ; ns, neural spines ; r, rays ; rb, rib ; sh, membranous basis of 

 vertebral centrum ; sp, scale pouches ; u, heemal cartilage into which the urochord pro- 

 jects ; vr, vertebral centra ; vt, ventral fl.n. 



Fig. 13.— Earliest embryo of Ganibusia as it lies in the follicle, x 22. 



Fig. 14. — Part of follicular membrane very much magnified, x 365. 



Fig. 15. — Cross-section through the tail of an advanced embryo, x 35. 



Fig. 16. — Longitudinal section through the anterior end of the incipient vertebral column of an ad- 

 vanced embryo, x 96. 



Fig. 17. — Longitudinal section through a branchial filament, x 183. 



Fig. 18. — The tail of an advanced embryo, drawn from sections, x 35. 



Fig. 19. — A vertebral segment and rib in place, from an advanced embryo, x 365. 



Fig. 20. — Neuromasts with their nerves from a cross-section through the cheek of an advanced embryo. 

 x200. 



