ON THE DEVELOPMENT OF LTMULUS LONGISPINA. 99 



Plate IX. 



Fig. 39. Portion of a transverse section of an embryo at the stage of fig. 12. 2C. 

 Fig. 40. Portion of a transverse section of an embryo, shown in fig. 18. 2C. 

 Fig. 41. Dorsal portion of a transverse section of an embryo, showing the 



cohimnar cells of the dorsum. 2D. 

 Fig. 42. Portion of a transverse section of an embryo, shown in fig. 10, showing 



the prominent lateral hump. 2D. 

 Figs. 43, 44. Dorsal, median portions of transverse sections of an embryo, at about 



the stage of fig. IG, showing the formation of the heart. 2D. 

 Fig. 45. Portion of a transverse section of an embryo, represented in fig. 17. 2C. 

 Fig. 40. Anterior portion of a longitudinal section, showing the peculiar cell 



group of the brain. 2D. 

 Fig. 47. Portion of a transverse section of an embryo, shown in fig. 13, through 



the fifth ganglia. IC. 

 Fig. 48. The same as above, cut throngh the sixth ganglia. IC, 

 Fig. 49. Longitudinal section of the second abdominal appendage, before the 



formation of the gill-lamellae. 2D. 



Plate X. 



Fig. CO. Median longitudinal section of an embryo at the beginning of the 



trilobite stage. 2ai. 

 Figs. 51, 52. Horizontal sections of an embryo in the same stage as above. 2aa. 

 Fig. 53. Horizontal section of the abdomen of an embryo of the trilobite stage. 



2aa. 

 Figs. 54, 55. Transverse sections through the abdomen of an embryo, a little more 



advanced than the one above mentioned. 2aa. 

 Figs. 5G, 57. Longitudinal sections of an embryo in the stage of fig. 17. 2aa. 



Plate XI. 



Fig. 58. Portion of a transverse section of an embryo, shown in fig. 14, through 



the coxopodite of the 5th appendage. 2C. 

 Fig. 59. Transverse section (a little oblique) of the cephalic region of an embryo, 



shown in fig. 12. 2B. 

 Fig, GO. Portion of a transverse section of an embryo, shown in fig. 13, through 



