484 



The Leptocardii, or Lancelets 



their actual common ancestry with the fishes, they must ap- 

 proach near to these in many ways. Their simplicity is largely 

 primitive, not, as in the Tunicates, the result of subsequent 

 degradation. 



The lancelets, less than a dozen species in all, constitute a 

 single family, Branchiostovnida;. The principal genus, Branchi- 

 ostoiiia, is usually called Amphioxus by anatomists. But while 



T'T ^„ *iiL_e 



2fe&^ 



Fig. 289. — California Laneelet, Branchiostoma calijorniense Gill. 

 (From San Diego.) 



the name Amphioxus, like laneelet, is convenient in vernacular 

 use, it has no standing in systematic nomenclature. The name 

 Braiichiostonia was given to lancelets from Naples in 1834, by 

 Costa, while that of Amphioxus, given to specimens from Corn- 

 wall, dates from Yarrell's work on the British fishes in 1836. 

 The name Amphioxus may be pleasanter or shorter or more 

 familiar or more correctly descriptive than Branchiostoma, but 

 if so the fact cannot be considered in science as affecting the 

 duty of priority. 



The name Acraniata (without skull) is often used for the 

 lower Chordates taken collectively, and it is sometimes applied 

 to the lancelets alone. It refers to those chordate forms which 

 have no skull nor brain, as distinguished from the Crauiota, 

 or forms with a distinct brain having a bony or cartilaginous 

 capsule for its protection. 



Origin of Lancelets. — It is doubtless true, as Dr. Willey sug- 

 gests, that the Vertebrates became separated from their worm- 

 like ancestry through "the concentration of the central nervous 

 system along the dorsal side of the body and its conversion 



