EXPLANATION OF PLATE 1 8. 459 



EXPLANATION OF PLATE 18. 



COMPLETE LIST OF REFERENCE LETTERS. 



Nervous System. 



a r. Anterior root of spinal nerve, n c. Neural canal. / r. Posterior root of 

 spinal nerve, sp n. Spinal nerve, sy g. Sympathetic ganglion. 



Alimentary Canal. 



al. Alimentary canal, al v. Caudal vesicle of the postanal gut. cl al. Cloacal 

 section of alimentary canal, dn. Duodenum, hpd. Ductus choledochus. pan. 

 pancreas, s as. Solid oesophagus, sp v. Intestine with rudiment of spiral valve. 

 umc. Umbilical canal. 



General. 



ao. Dorsal aorta, aur. Auricle of heart, ca v. Cardinal vein. ch. Notochord. 

 eppp. Epithelial lining of the body-cavity. ir. Inteirenal body. me. Mesentery. 

 mp. Muscle-plate, m p I. Muscle-plate sending a prolongation into the limb, p o. 

 Primitive ovum. pp. Body-cavity. s d. Segmental duct. s t. Segmental tube. 

 / s. Tail swelling, v can. Caudal vein. x. Subnotochordal rod. 



Fig. i. 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 (nip 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. i. 

 The section is taken through the region of the heart, so that the cavity of the auricle 

 (aur) 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 belonging to stage 

 K, shewing the condition of the postanal section of the alimentary tract. Zeiss A, 

 ocul. 2. An explanation of these figures is given on p. 449. 



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. 



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