INTERNAL ANATOMY. 



73 



which has been observed in some craniate Vertebrates as 

 described above, is therefore probably of the same nature 

 as the ectodermic openings of the tubules in Amphioxus. 



Fig. 35. A. Schematic transverse section through pharyngeal region of Am- 

 phioxus. On the left is a branchial bar, cut lengthwise, and on the right a gill-slit. 



B. Schematic transverse section through Selachian embryo. (After BOVERI.) 



at.c. Atrial chamber, p.n.d. Pronephric duct. c.o. Nephrostome of pronephric 

 tubule, k.t. Cross-section of excretory tubule in Amphioxus. a.f. Opening of 

 excretory tubule into atrium in Amphioxus. g.c. Gonadic cavity (perigonadial 

 coelom) in A ; compared by Boveri with the mesonephric tubule, mes.t. in B. 

 gl. Glomerulus. ca>. Ccelom. e.c. Endostylar ccelom. s.i.v. Branchial artery in 

 A ; sub-intestinal vein in B. 



Other letters as in previous figures. 



N.B. In B the future opening of the mesonephric tubule into the pronephric 

 duct is indicated by dotted lines on the right. The vessel connecting the sub- 

 intestinal vein with the aorta is placed on the left of the alimentary canal for com- 

 parison with Fig. A. It is really only present on the right side, although a rudiment 

 occurs on the left. (See Note 6.) 



The glomeruli of the tubules in Amphioxus are supplied 

 by blood-vessels which connect the dorsal aorta with the 

 branchial artery. It should be remembered that the bran- 

 chial artery represents the anterior portion of the sub- 



