xlviii EXPLANATION OF PLATES 37, 38. 



PLATE 37. 



Fig. 39. Section through the olfactory involution and part of fore-brain of a 

 larva on the ninth day after impregnation, shewing olfactory nerve. 



Fig. 40. Section through the anterior part of the head of the same larva, shewing 

 pituitary involution. 



Figs. 41 43. Transverse sections through an embryo on the eleventh day after 

 impregnation. 



Fig. 41. Through fore-part of head, shewing the pituitary body still con- 

 nected with the oral epithelium. 



Fig. 42. Slightly further back than fig. 41, shewing the pituitary body 

 constricted off from the oral epithelium. 



Fig. 43. Slightly posterior to fig. 42, to shew olfactory involution, eye, 

 and hyomandibular cleft. 



Fig. 44. Longitudinal section of the head of an embryo of 1 5 millims. in length, 

 a few days after hatching, shewing the structure of the brain. 



Fig. 45. Longitudinal section of the head of an embryo, about five weeks after 

 hatching, 26 millims. in length, shewing the structure of the brain. In the front part 

 of the brain the section passes slightly to one side of the median line. 



Figs. 46 A to 46 G. Transverse sections through the brain of an embryo 25 

 millims. in length, about a month after hatching. 



Fig. 46 A. Through anterior lobes of cerebrum. 



Fig. 46 B. Through posterior lobes of cerebrum. 



Fig. 46 C. Through thalamencephalon. 



Fig. 46 D. Through optic thalami and optic chiasma. 



Fig. 46 E. Through optic lobes and infundibulum. 



Fig. 46 F. Through optic lobes and cerebellum. 



Fig. 46 G. Through optic lobes and cerebellum, slightly in front of fig. 46 F. 



PLATE 38. 



Figs. 47 A, B, C. Figures of adult brain. 

 Fig. 47 A. From the side. 

 Fig. 47 B. From above. 

 Fig. 47 C. From below. 



Fig. 48. Longitudinal vertical section through the eye of an embryo, about a 

 week after hatching, shewing the vascular membrane surrounding the vitreous 

 humour. 



Fig. 49. Diagram shewing the arrangement of the vessels in the vascular mem- 

 brane of the vitreous humour of adult eye. 



Fig. 50. Capillaries of the same vascular membrane. 



Fig. 51. Transverse section through anterior part of trunk of an embryo on the 

 ninth day after impregnation, shewing the pronephros and pronephric chamber. 



