CRANGON VULQARIS. 



41 



n 1 antennular nerve. 



n 2 antennal nerve. 



n* first maxillary nerve. 



na neural blastema. 



nc nerve cells undergoing 

 metamorphosis into 

 nerve fibres. 



nc 1 nerve cells of optic gang- 

 lion. 



oc ocellus. 



oe oesophagus. 



of fibres of second antennal 

 nerves. 



og optic ganglion. 



oi optic invagination. 



ol optic lobe. 



om ommatidial layer of eye. 



os ostiole of heart. 



p proctodeutn. 



pf pyloric fold. 



pg pigment. 



py pyloric portion of stom- 

 ach. 



r rostrum. 



rp retinophora. 



sg supra-oasophageal gang- 

 lion. 



sn Semper's nuclei. 



so somatoplure. 



sp splanchnoplure. 



st stomodeum. 



t thorax (telson in fig. 20). 



ta thoracic abdominal area. 



te telson. 



vm ventral mesoderm. 



y yolk. 



Fig. 28. Diagram of egg in " Stage A," to show the planes of the 

 sections. By an error, two of the planes are wrongly numbered ; the 

 figures 30 and 31 should be transposed. 



Fig. 29. Obliquely longitudinal section of stage A passing through 

 the anus and through the inner edge of the optic lobe. 



Fig. 30. Transverse section of the same stage behind the abdominal 

 flexure. 



Fig. 31. Transverse section of the same stage cutting through both 

 nerve bands. 



Fig. 32. Diagram of the embryo in stage C to show the planes of 

 section of figures 33 to 37 and 41. (The curvature of the lines is due 

 to an attempt to show "great circles" on a plane.) 



Fig. 33. Tranverse section passing through the anterior portion of 

 the optic lobes of "stage C." 



Fig. 34. Same, a little farther back. This and the preceding fig- 

 ure show the separation of the optic and cerebral ganglions. 



Fig. 35. Section of same stage, passing behind the mouth and cut- 

 ting the oesophagus and first appendage. 



Fig. 36. Sagittal section of the same stage. (This egg was consid- 

 erably contracted and the proportions are not quite as in the normal 

 condition.) 



Fig. 37. Obliquely longitudinal section of a slightly older stage in 

 which the mesoderm has extended in front of the eye. 



Fig. 38. Longitudinal section through stage D. 



Fig. 39. "Dorsal organ" of stage C (Compare fig. 37). 



ESSEX INST. BULLETIN, VOL. XXI. 3* 



