lot 



THE ANATOMY OF VERTEBRATED ANIMALS. 



I. The PHAETNUOBEAircHn. — ^This order contains but one 

 species of fish, the remarkable Lancelet, or Amphioxus 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 liard 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,/", g). 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 



PLC, 2S. — AmpJiioxv^ lanceolaUis.~a, mouth; 6, pharyngobranchial chamber; c, anus; 

 d, liver ; «, abdominal pore. — B, tlie head enlarged ; a, the notochord ; ft, the represent- 

 atives of neural spines, or fin-rays; c, the jointed oi-al ring ; rf, the filamentary append- 

 ages of the mouth; *?, the eihated lobes of the pharj'nx ; /, 17, part of the branchial sac 

 \ the spinal cord. 



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

 an Ascidian (Fig- 28, B, /, g). Tliis great pharynx is con 

 nected with a simple gastric cavity which passes intr i. 



