EXPLAXATIOX OF PLATE XII. 



Complete list of reference letters. 



ep. epiblast. sp. c. spinal cord. 1 1, lateral line. 



sp. g. spinal ganglion. m. c. mucous canal of the head. 



71. I. uervus lateralis. v. in. intestinal branch of the vagus. 



r. 0]). ramus ophthalmicus of the fifth nerve. 



m. p. muscle-plate. m. p' . muscles of muscle-plate. 



V. ar. vertebral arch. na. neural arch. ha. haemal arch. 



rp. rib process. m. el. membrana elastica externa. 



V h. vertebral body. ch. notochord. sh. sheath of notochord. 



X. sub-notochordal rod. )<ij. g. sympathetic ganglion. 



s. d. segmental duct. I. liver. al. alimentary tract. 



um. ductus choledochus. ao. aorta. ca v. cardinal vein. 



T. can. caudal vein. v. blood-vessel. c. connective tissue. 



Fig. 1. Section through the anterior part of an embryo of Scyllium 

 canicula during stage L. 



c. Peculiar krge cells which are found at the dorsal part of the spinal 

 cord. Sympathetic ganglion shewn at sij. g. Zeiss A, ocul. 1. 



Fig. 2. Section through the lateral line at the time of its first formation. 

 The cells marked n. I. were not suflBciently distinct to make it quite 

 certain that they really formed part of the lateral nerve. Zeiss B, ocul. 2. 



Fig. 3rt. 3?>. 3 c. 3f/. Four sections of the lateral line from an embryo 

 belonging to stage L. 3n^ is the most anterior. In 3« the lateral nerve 

 {n. I.) is seen to he in the mesoblast at some little distance from the lateral 

 line. In 3b and 3c it lies in immediate contact with and partly enclosed 

 by the modified epiblast cells of the lateral hue. In 3^/, the hindermost 

 section, the lateral line is much larger than in the other sections, but no 

 trace is present of the lateral nerve. The sections were taken from the 

 following slides of my series of the embryo (the series commencing at the 

 tail end) 3c/ (46). 3c (64). Sb (84). 3a (93)." The figures all drawn on the same 

 scale, but 3 a is not from the same side of the body as the other sections. 



Fig. 4. Section through lateral line of an embryo of stage P at the 

 point where it is acquiring an opening to the exterior. The peculiar 

 modified cells of its innermost part deserve to be noticed. Zeiss D, ocul. 2. 



Fig. 5. Mucous canals of the head with branches of the ramus ophthal- 

 micus growing towards them. Stage 0. Zeiss A, ocul. 2. 



Fig. 6. Mucous canals of head with branches of the ramus ophthal- 

 micus gi'omng towards them. Stage between and P. Zeiss aa, ocul. 2. 



Fig. 7. Junction of a nerve and mucous canal. Stage P. Zeiss D, 

 ocul. 2. 



Fig. 8. Longitudinal and horizontal section through the muscle-plates 

 and adjoining structures at a stage intermediate between L and M. The 

 section is intended to shew the gradual conversion of the cells of the 

 somatic layer of muscle-plates into muscles. 



Fig. 9. Longitudinal section through the notochord and adjoining 



