n8 



A NATURAL HISTORY OF THE SEAS 



Why the Ascidians, having travelled so fat upon the 

 road of evolution, should cease to progress and degenerate 

 is at present one of the many unsolved problems of the 

 biologist. Even their origin is pure conjecture, since 

 fossil remains of any soft-body creatures are extremely 

 rare and of these none have anything recognisable as 

 Ascidians have as yet come to light. 



Somewhere between the Ascidians and the Fishes may 

 be placed that strange little creature known as the Lancelet 

 or Ampbioxus. Several species are abundant on sandy 



Notochord 



•..*« 



Mouth 



Fins 



Exhalent oriFIce 



Lancelet (Ampbioxus) 



shores in most warm seas, the first Lancelet being recog- 

 nised by the Cornish naturalist Couch, who discovered 

 our native species on the south-west coast just over a 

 century ago. 



As the name Ampbioxus implies, the creature is pointed 

 at both ends. It is flattened, leaf-like, and glassy, and the 

 largest species attains to only a few inches in length. 

 If compelled to exert itself, it swims feebly for a few feet, 

 then sinks as though exhausted to the bottom, quickly 

 hiding itself in the sand. It comes out chiefly at night, 

 and the sexes though separate are distinguishable only by 

 a microscopic examination. 



