FlG. 17. — Transverse section 

 through head of normal trout embryo, 

 showing cerebellum, auditory organs, 

 medulla, pharynx, gill chambers, etc. 

 Compare with PI. XIV. fig. 51 (union 

 at medulla). For other references see 

 under PI. I. fig. r. ( x 15.) 





FlG. 18. — Transverse section 

 through head of normal trout embryo, 

 -1). wing the posterior part of the 

 medulla, the gill chambers, and the 

 anterior part of the heart. Compare 

 with PI. IX. fig. 38 (union at optic 

 lobes). For other references st'e under 



pi. 1. fig. 1. (X15.) 



FlG. 19. — Transverse section of nor- 

 mal trout embryo in pectoral region. 

 The section passes through the head- 

 kidney, oesophagus, and pectoral fin. 

 Other references under PI. I. fig. 1. 

 (xi50 



Fig. 20. — Transverse section of nor- 

 mal trout embryo, across middle of 

 body, showing swim-bladder, intestine, 

 and pancreatic tissue. The specimen, 

 which is otherwise normal, shows local 

 reduplication of the notochord. See 

 p. 5^. Other references under PI. I. 

 fig. 1. (xi5.) 



PL. IV 



