140 MALCOLM LAURIE. 



Fig. 30. — Longitudinal section to one side of the middle line, showing the 

 appendages and ccElomic spaces, x -^~-. 



Fig. 31. — Transverse section through the third somite of Stage I, showing 

 the formation of the appendage, the neural thickening, &c. x -'\^. 



Fig. 32. — Surface view of embryo at Stage K, showing the cerebral invagi- 

 nations, abdominal appendages, tail, &c. X --^. 



Fig. 33. — Transverse section through the base of a thoracic appendage, 

 showing the sternocoxal process. 



Fig. 3'±, a — /i. — Series of sections through base of fifth appendage, showing 

 the coxal gland. 



Fig. 35. — Transverse section through one of the abdominal appendages and 

 the tail, showing the appendage, the neural thickening beginning to separate 

 from the epiblast, the gut forming in the tail, &c. X -V- 



FiG. 36. — Transverse section through the cephalic segment of a somewhat 

 earlier embryo, showing the beginning of the cerebral invagination, x -^ . 



Fig. 37, a — d. — Sections through the head of an embryo of Stage K, show- 

 ing the cerebral-optic invaginations, x -^ . 



^ PLATE XVII. 



Fig 38. — Surface view of an embryo of Stage L extended in a plane, 

 showing the cerebral invagination, the central eyes, &c. x -\°-. 



Fig. 39. — Transverse section through the base of the fifth appendage, 

 showing the coxal gland, x -V"- 



Fig. 40. — Section through the pectines. x -\§- . 



Fig. 41. — Section through an abdominal appendage, showing the inpushiug 

 to form the gill-book, x -''-^ . 



Fig. 42, a, b. — Transverse sections through the cerebro-optic invaginations. 

 X -^. 



Fig. 43. — Longitudinal section through the cerebro-optic invaginations, 

 showing the formation of the brain and the central eye. X ^4^. 



Fig. 44. — Surface view of an embryo of Stage M, from the ventral surface. 

 X -\"-. 



Fig. 45.— Surface view of the dorsal side of the head of the same embryo, 

 showing the central and lateral eyes, x -\"-. 



Fig. 46. — Section through the seventh somite, showing the formation of 

 the genital tube from part of the ccclom. x -^. 



Fig. 47.-^Longitudinal sccion through a gill-book, showing the commence- 

 ment of the formation of the lamellae. X -^J-. 



Fig. 48. — Longitudinal section through the head end, showing the stomo- 

 dseum and the cerebro-optic invagination from which the brain is now entirely 

 separate, x -^- . 



Fig. 49. — Transverse section through the same region, x -^V-- 



