20 S. F. CLARKE. 



Figure 15 — Conlinved. 



in connective tissue-like cortiuscles, wliich appear first 

 in the dorsal region ; py, yellow pisment in small cells 

 resembling ordinary epithelium cells ; df, dorsal fin ; 

 vf, ventral fin. 



PLATE 3. 



Figure 16 is enlarged 12 diameters. 

 Figures 17 to 20 are enlarged 10 diameters. 



Figure 16. — A lateral view; f, depression in which mouth is formed ; 

 bl, balancer; h, pericardial region; n. p. nasal pit; 

 a. I. abdomen; v. f. ventral fin; d. f. dorsal fin; ii.f. 

 and n. t. neural or spinal region. The most rapid 

 centres of growth at this period are the tail, dorsal fin, 

 branchise and balancers. 



Figure 17. — Ventral view a day or two later than that of Figure 16. 

 The region between the nasal pits and the anterior end 

 of the body has been imperfectly represented in the 

 figure. It is simply rounded. The position of the 

 mouth is distinctly indicated by the groove m ; the 

 throat is clearly marked ofi' from the body by a suture 

 or depression ; the balancers are developing rapidly 

 and have become capitate; the branchiae are much 

 elongated and are budding out lateral processes ; the 

 lobes of the anterior limbs show signs of active growth 

 once more ; a, the anus. The heart cau no longer be 

 seen through the thickened integument. 



Figure 18. — A dorsal view; n. t. external indication of outline of 

 brain cavity; fia, lobe of anterior limb. The caudal 

 region has much increased in length ; the branchiae 

 are longer and have acquired numerous processes of 

 considerable length. The limb-lobes are also more 

 elongated. 



Figure 19. — Represents the anterior end only; hal, balancer, now 

 completely developed; bn, branchiae; b. s. branchial 

 stump, the gill having been cut away to show the ante- 

 rior limb ; 6. a. the anterior limb. The latter is now 

 much elongated, the elbow-joint is indicated and the 

 first and second digits. 



Figure 20. — The same as Figure 19, but with the branchiae not cut 

 away. 



