212 THE EMBRYOLOGY OF THE TELEOSTS. 



Figs. 25, 26 27. Three stages in formation of notoohord shown in (optical) section. 



Fig. 28. Same at later stage. 



Fig. 29. Siile view of embryo, etc., showing the blastoderm with (faintly) its thickened margin. 



Fig. 30. Oblique view of tail end of fig. 29, showing the neural groove, the tail swelling and the thick- 

 ened ma'rgin of the blastoderm, the slight notch in the margin at t s may possibly represent the neurenteric 

 canal. 



Fig. 32. Formation of optic lobes and protovertebrae ; the apparent distortion of the figure is due to an 

 attempt to represent the embryo in perspective. 



Fig. 33. Stage a little later than 32 showing optic lobe and mesenteron and a few of the anterior proto- 

 vertebrae. 



Fig. 34. Still later with fore-, mid- and hind-brain differentiated and pericardial region forming. 



Fig. 35. Splitting of mesoblast into somatopleure and splanchnopleure. 



Fig. 36. Dorsal view of head a little later than fig. 34 with formation of the lens of the eye and the 

 appearance of the lumen in the brain and optic vesicles. 



Figs. 37, 38, 39. Successive changes in appearance of notochord. 



PLATE XVI. 



Fig. 40. Heart and blood vessels in stage nearly corresponding with fig. 51, or shortly before hatching. 



Fig. 41. Relations of notochord, aorta, urogenital canal, mesenteron and proctodeum in hatched fish. 



Fig. 42. Lumen in mesenteron in embryo about like fig. 43. 



Fig. 43. Embryo with the lens of the eye, auditory vesicle and nasal pits well advanced. The blasto- 

 derm has closed and the tail has begun to grow out. Kupffer's vesicle was present but is omitted in the 

 drawing. 



Fig. 44. Anal region in hatched fish. 



Fig. 45. Details of head in fig. 43. 



Figs. 46 and 47. Out-growth of liver in its earliest stage from the side and from beneath. 



Fig. 48. Anterior portion of fish two days old from beneath, showing anterior end of urogenital canal. 

 The stomodeum and mesenteron have not yet met. H. W. Conn, del. 



Figs. 49 and 50. Fish of about four days. H. W. Conn, del. 



Fig. 51. Embryo of unknown teleost just before hatching: 



Fig. 52 and 54. Two stages in formation of Kupffer's vesicle, u, seen in optical section. 



Fig. 53. Fish between four and five days old. 



