EXPLANATION OF PLATE XVIL 



Complete list of reference letters. 



Nervous System. 



sy. g. sjTiipathetic ganglion. sp. n. spinal nerve. 



p r. posterior root of spinal nerve. a r. anterior root of spinal nerve. 



71. c. neural canal. 



Alimei^tary Canal. 

 al. alimentary canal. iitn. c. umbilical canal. 

 hp. d. ductus choledochus. clu. duodenum. ji?a?i. pancreas. 

 sp. V. intestine with rudiment of spiral valve. s. oes. solid oesophagus. 

 al. V. caudal vesicle of the postanal gut. cl. al. cloacal section of ali- 

 mentary canal. 



Gexeral. 

 mp. muscle-plate. 



mp.l. muscle-plate sending a prolongation into the limb. 

 s t. segmental tube. s d. segmental duct. ca. v. cardinal vein. 

 V. cau. caudal vein. ao. dorsal aorta. aur. auricle of heart. 

 ch. notochord. p o. primitive ovum. ir. interrenal body. 

 j9/?. body-cavity. ep.p>p. epithelial lining of the body-cavity. 

 me. mesentery. t. s. tail swelling. x. subnotochordal rod. 



Fig. 1. Transverse section through the anterior abdominal region of 

 an embryo of a stage between K and L. Zeiss B, ocul. 2. Reduced 

 one-third. 



The section illustrates the junction of a sympathetic ganglion with a 

 spinal nerve and the sprouting of the muscle-plates into the limbs {mp. I). 



Fig. 2. Transverse section through the abdominal region of an embryo 

 belonging to stage L. Zeiss B, ocul. 2. Reduced one-third. 



The section illustrates the junction of a sympathetic ganglion with a 

 spinal nerve, and also the commencing formation of a branch from the 

 aorta (still solid) which will pass through the sympathetic ganglion, and 

 forms the first sign of the conversion of part of a sympathetic ganglion into 

 one of the suprarenal bodies. 



Fig. 3. Longitudinal and vertical section of an embryo of a stage 

 between L and M, shewing the successive junctions of the spinal nerves 

 and sympathetic ganglia. 



Fig. 4. Section through the solid oesophagus during stage L. Zeiss 

 A, ocul. 1. The section is taken through the region of the heart, so that 

 the cavity of the auricle {aiir) lies immediately below the oesophagus. 



Fig. 5. Optical section of the tail of an embryo between stages I and 

 K, shewing the junction between the neural and alimentary canals. 



Fig. 6. Four sections through the caudal region of an embryo belong- 

 ing to stage K, shewing the condition of the postanal section of the 

 alimentai7 tract. Zeiss A, ocul. 2. An explanation of these figures is given 

 on p. 220. 



Fig. 7. Section through the interrenal body of a Scyllium embryo 

 belonging to stage Q. Zeiss C, ocul. 2. 



Fig. 8. Portion of a section of the interrenal body of an adult 

 Scyllium. Zeiss C, ocul. 2. 



