?2, 



Pig. 47. A similar section showing the po^xchos separate. 

 Pig. 48. Transverse section of an embryo about 45 hours 



old, ta]-cen where the storaodaeum Joins the midgut, 

 Pig. 49, Transverse section of the same embryo a little 



further posterior. 

 Pig. 50. Section of the gill rudiment in the plane indi- 

 cated by the line 50, figure 36, 

 Pig, 51. Section of the same gill rudiment in the plane 



indicated by the line 51, figure 36. 

 Pigs, 52, 53 and 54. Transverse sections showing tho 



formation of the "sole" of the foot. 

 Pig, 55, Median, vertical section of an embryo about 95 



hoxirs old. (A portion of the stomodaeum was 



drawn from the next section). 

 Fig, 56. Transverse section of an embrj'"© about 75 hours 



old, showing the invaginations that form the 



otocysts. 

 Pig, 57, Transverse section of an embryo about 70 hotirs 



old showing the forming pedal ganglia. 

 Pigs. 58, 59 and 60. Successive tran.sverse sections 



through the anterior portion of an ombrsT'o about 



95 hours old. 



