[ON Ol PLATE 1 3. xxi 



.in partially filled with 

 bodies resembliiu; 



nt.il .ui.l l.>m;itiii!in.il sci ryo In-longing to 



A.ocul. i. : i<! |n-|Mi. Active-tissue- cell* arc 



omitted. 



The section shews ih.it th- egmcntal tulx: to each vertebral si-gii:- 



17. Portion of .! Srylliuin embiyo belonging to Mage K, vi<-w< d as a trans- 

 parent ob- 

 it shews the segincntal duct and the segmental involutions two of which are seen 

 to belong to .segments behind the end of the alimentary 



Ki-. 18. Vertical longitudinal section of a Scyllium embiyo belonging to Mage K. 

 Xeiss A, ocul. i. Hardened in a mixture of osinic and chroinii- I .e.W8 



(1) the commissures connecting together the posterior mots of the spinal nerves; 



(2) the junction of the anterior and poster 



(3) the relations of the segmental ducts to the segmental involutions and the 



alternation of calibre in the segmental tu 



(4) the germinal epithelium lining the body-cavity. 



EXPLANATION OF PLATE 13. (X. p. 361.) 



COMPLETE LIST OF REFERENCE LETTERS. 



aL Alimentary tract, ao. Aorta, c. Connective tissue, cav. Cardinal vein. 

 ch. Notochord. ep. Epiblast. ha. Haemal arch. /. Liver. //. Lateral line. me. 

 Mucous canal of the head. mel. Membrana elastica externa. ////. Muscle-plate. 

 m p' '. Muscles of muscle-plate, na. Neural arch. /;/. Nervus lateralis. rp. Rib 

 process, s d. Segmental duct. sh. Sheath of notochord. spc. Spinal cord, sp g. 

 Spinal ganglion, syg. Sympathetic ganglion, urn. Ductus choledochus. v. Blood- 

 vessel, var. Vertebral arch. vb. Vertebral body, vcait. Caudal vein. ~ in. In- 

 testinal branch of the vagus, v op. Ramus ophthalmicus of the fifth nerve. JT. Sub- 

 notochordal rod. 



Fig. i. Section through the anterior part of an embryo of Scyllium canicula 

 during stage L. 



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

 Sympathetic ganglion shewn at syg. Zeiss A, ocul. i. 



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



The cells marked n I were not sufficiently distinct to make it quite certain that 

 they really formed part of the lateral neiv< . . ocul. i. 



Figs. 30, 3^, 3^, $d. Four >ection> <>f the lateral line from an embryo belonging 

 to stage L. $a is the most anterior. In ^a the lateral nerve (nl) is seen to He in the 

 mesoblast at some little distance from the lateral line. In 3^ and $c it lies in 

 immediate contact with and partly enclosed by the modified epiblast cells of the 

 lateral line. In 3 d, 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) $d (46), 3^ (64), 3 b (84), 3 a (93). The figures all drawn on the same 

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



