io A Guide to the Zoological Collections 



peribranchial or atrial cavity, whence it is discharged 

 by a special opening, situated in the middle line some 

 way in front of the anus, known as the atrial opening 

 or atriopore ; while the food is caught and carried, by 

 structures corresponding with the endostyle and dorsal 

 lamina of the Tunicates, into the alimentary canal, 

 whence the undigested waste escapes at the anus. 



The atriopore is indicated by a pointer in one of the 

 specimens, the anus by a red circle. 



Drawing No. i shows (i) the long smooth compressed 

 lancet-like body tapering to a sharp point at both ends 

 (whence the name Amplii-oxus) and showing no distinc- 

 tion whatever of head, trunk, and tail : (2) the long fold 

 of skin, or dorsal fin, running from the right side of the 

 mouth all along the middle line of the back, and its 

 gelatinous fin-rays ; the short fold, or ventral fin, run- 

 ning between the atriopore and the anus, and its fin- 

 rays ; and the caudal fold or fin, connecting the other 

 two round the end of the tail : (3) the V-shaped muscle- 

 segments extending in a chain from one end of the body 

 to the other, but leaving exposed, at either end, the tip 

 of the (4) notochord. [This, which is seen in section in 

 Drawing No. 2, is a solid elastic rod of semi-cartilagi- 

 nous consistence that extends all along the middle of 

 the back, and is all that Amphioxus possesses in the 

 way of a true skeleton] : (5) the mouth, at the fore-end 

 of the body, encircled by small stiff oral tentacles: (6) 

 the anus, which lies a little to the left of the middle line, 

 near the after end : (7) the atriopore, some little way in 

 front of the anus: (8) the series of reproductive organs, 

 or gonads, showing through the semi-transparent body- 

 wall. 



Drawing No. 2 is meant to show specially : — (1) 

 the position and form of the notochord : (2) the posi- 



