EXPLANATION OF PLATES XllI, TLY— Continued. 



Fig. 23. — Longitudinal and horizontal section through the head, showing 

 fore- and hinclbrain, third and trigeminal nerves, eyes and olfactory pits. 

 X 20 diam. 



Pig, 24. — Transverse section through forepart of body, showing spinal 

 cord, with anterior and posterior roots of a spinal nerve, vagus nerve, 

 cardiac and dorsal aorta, branchial arteries, pharynx and gills. X 20 diam. 



Pig. 25. — The right olfactory organ fi-om the same section as fig. 23 

 more highly magnified, showing the characters of the Schneiderian folds. 

 X 90 diam. 



Pig. 26. — The left gill from fig. 2i more highly magnified, showing 

 histological characters of the gill folds, x 90 diam. 



Pigs. 27 and 28. — Sections from a dogfish embryo about stage o, showing 

 resemblance between gills and Schneiderian folds at a rather later period. 

 X 90 diam. 



Pig. 27. — Through Schneiderian folds. 



Pig. 28.— Through gill. 



Fig. 29. — Transverse section through the anterior extremity of the head 

 of a trout embryo on the twenty-seventh day after fertilisation of the ova, 

 showing forebrain, olfactory pits, and on the left side the olfactory nerve. 

 Picric acid. X 56 diam. 



Pig. 30. — Longitudinal and vertical section through the head of a trout 

 embryo on the thirtieth day, showing mid- and hindbrains, roots of visceral 

 arches and clefts, and the olfactory pit. Picric acid, x 56 diam. 



Pig. 31. — Transverse section through the anterior extremity of the head 

 of a salmon embryo about the time of hatching, showing olfactory pits, 

 trabecular plate, and anterior prolongations of the buccal cavity. Chromic 

 and osmic acids. X 27 diam. 



Pig. 32. — Transverse section through the forepart of the head of a 

 salmon embryo about a week after hatching, showing forebrain, eyes, 

 olfactory pits, and paired-anterior diverticula of the buccal cavity. Picric 

 acid. X 27 diam. 



Pig. 33. — Transverse section through the forepart of the head of a salmon 

 embryo two days after hatching, showing forebrain, and on the left side tlie 

 eye, on the right the olfactory nerve and organ. Chromic and osmic 

 acids, X 35 diam. 



Pigs, 34 and 35, — Longitudinal and vertical sections through the head of 

 a salmon embryo of the same age as that in the preceding figure. Chromic 

 and osmic acids. X 27 diam. 



Pig. 34. — Section taken close to median line, showing root of olfactory 

 nerve, optic nerves, infundibulum, and anterior prolongation of buccal 

 cavity. 



Pig. 35. — More superficial section, showing olfactory pit, eye, pharynx 

 with its branchial arches, and the anterior prolongation of the buccal 

 cavity. 



Pig. 36. — Longitudinal and vertical section through the forepart of the 

 cerebral hemisphere, the olfactory lobe and olfactory nerve of a twelve-day 

 chick embryo. Picric acid, x 17 diam. 



Pigs. 37, 39 — Transverse sections through same region as preceding 

 figure in a twelve-day chick embryo. Picric acid, x 17 diam. 



Pig, 37. — Through the olfactory nerve. 



Pig, 38, — Through the olfactory lobe. 



Pig. 39. — Through the anterior part of the cerebral hemisphere. 



