104 



THE ANATOMY OF VERTEBRATED ANIMALS. 



I. The PHARY]srGOBRA:N^CHn. — This order contains but one 

 species of fish, the remarkable Lancelet, or Am^^hioxus lanceo- 

 latus, which lives in sand, at moderate depths in the sea, in 

 many parts of +he world. It is a small, semitransparent crea- 

 ture, pointed at both ends, as its name implies, and possessing 

 no limbs, nor any hard epidermic or dermal covering-. 



The dorsal and caudal regions of the body present a low 

 median fold of integument, which is the sole representative of 

 the system of the median fins of other fishes. The mouth 

 (Fig. 28, A, a) is a proportionally large oval aperture, which 

 lies behind, as well as below, the anterior termination of the 

 body, and has its long axis directed longitudinally. Its mar- 

 gins are produced into delicate ciliated tentacles, supported by 

 semi-cartilaginous filaments, which are attached to a hoop of the 

 same texture placed around the margins of the mouth (Fig. 

 29,/",^). These probably represent the labial cartilages of 

 other fishes. The oral aperture leads into a large and dilated 

 pharynx, the walls of which are perforated by numerous 



Fig. 28. — AmpJdoxus lanceolatus. — a, mouth; 5, pliar}Tijrobranchial chamber; c, anus; 

 d, liver; «, abdominal pore. — B, the head enlarged ; o, the notochord ; b, the represent- 

 atives of neural spines, or fin-rays; c, the jointed oral ring ; (f, the filamentary append- 

 ages of the mouth ; e, the cihated lobes of the ijharj'iix ; /; gr, part of the branchial sac ; 

 A, the spinal cord. 



clefts, and richly ciliated, so that it resembles the pharynx of 

 an Ascidian (Fig. 28, B, /*, g). This great pharynx is con 

 nected with a simple gastric cavity which passes into l 



