BONY-FISH. 27 



lar tissue, tracing its branches (afferent branchial arteries} 

 into the gill-arches (p. 24). What relations do these 

 branchial arteries and ventral aorta bear to the pharynx? 



Now cut away the floor of the throat and trace in the 

 gill-arches the efferent branchial arteries to their union 

 above the gullet in the longitudinal blood-vessel , the dorsal 

 aorta. Can you find this aorta in the roof of the peritoneal 

 cavity? Could the blood-system, so far as you have studied 

 it, be described as two longitudinal vessels lying on either 

 side of the alimentary canal, and connected by a series of 

 paired transverse vessels? What must be the course of 

 the blood in the different parts of the system? Draw a 

 diagram illustrating the relations of the circulatory appa- 

 ratus to the alimentary canal and gill-slits. 



Pick into the side of the tail until the back-bone (vertebral 

 column) is reached. Take out a small piece of it and clean 

 it by boiling a few minutes in a beaker or test-tube.* 

 Wash away the flesh, and see that it is made up of a series 

 of bones (vertebra?), arranged one after the other. Exam- 

 ine a single vertebra, making out the following parts: 

 (1) A body or centrum, shaped like an hour-glass and 

 hollow at either end (amphiccelous) . Do the hollows of 

 the two ends connect? (2) Arising from the centrum 

 two bony plates (neural processes), uniting above into a 

 single neural spine. These together form a neural arch; 

 so called, since the great nervous (neuron, nerve) struc- 

 ture, the spinal cord, passes through it. (3) On the oppo- 

 site or ventral side of the centrum a similar hcemal arch, 

 composed of hcemal processes and hcemal spine, so called 

 because the caudal blood-vessels pass through the arch 

 (haima, blood). 



* A few vertebrae from the table will answer equally as well. 



