200 MARINE AND FRESHWATER FISHES^ 



feature common to ordinary fishes, with the exception that 

 a slender fold of integument representing a rudimentary 

 dorsal fin is developed along the back, and that the body sub- 

 stance is similarly divided by faint oblique lines into distinct 

 muscle regions or " myotomes." The mouth is a largish 

 oval aperture developed beneath the anterior termination 

 of the body, and having its margin bordered with a series of 

 delicate ciliated tentacles. The mouth conducts to a largely 

 dilated pharynx perforated with numerous clefts, the walls 



FIG. 33. LANCELET (Amphioxus lanceolatus). 



of which are richly ciliated, and have the blood vessels dis- 

 tributed upon them after the manner of the pharynx of an 

 Ascidian. Following upon the pharynx is a simple stomach 

 or gastric cavity that passes into a straight intestine and 

 terminates near the root of the tail in the anal aperture. 

 Such are the leading features of this remarkable animal, 

 which, so far as our present knowledge extends, represents 

 the dawning form or Architype of all Piscine life, and still 

 retains structural features that unite it closely with the 

 lower classes of backboneless animals or Invertebrata. 



