CHAPTER IV 



CEPHALOCHOEDATA 



INTEODUCTION GENERAL CHARACTERS — -ANATOMY OF AMPHIOXUS 



EMBRYOLOGY AND LIFE-HLSTORY CLASSIFICATION OF 



CEPHALOCHORDATA SPECIES AND DISTRIBUTION 



The CEPHALOCHORDATA Comprise only a small group of little 

 fish -like forms, the Lancelets, usually known as " Amphi- 

 oxus," and referable to about a dozen species arranged in 

 several closely allied genera under the single family Branchiosto- 

 matidae. The best known form is Brancliiostoma lanceolatum 

 (Pallas), the common Amphioxus or Lancelet, which has been 

 found in British seas, and even as far north as the coast of 

 Norway, but is much more common in warmer waters, such as the 

 Mediterranean, and is also found in the Indian Ocean. It is 

 abundant in the Bay of Naples, and lives and breeds in great 

 numbers in a salt lagoon, the " Pantano," near Messina, and from 

 these localities most of the specimens have been obtained for the 

 numerous recent researches upon its structure and development. 



Amphioxus was first discovered and described (1778) by 

 Pallas, who regarded it as a Mollusc, and named it Limax 

 lanceolatus. It was first correctly diagnosed as a low Vertebrate, 

 and named Brancliiostoma, by Costa, in 1834. The term 

 Amphioxtis, under which it has become so well known, was 

 applied to it a couple of years later by Yarrell. 



The anatomy was for the first time fully investigated by 

 Johannes Miiller in 1841, and this important memoir has been 

 supplemented in regard to special systems and histological 

 details by numerous papers by many leading zoologists, such as 

 those by Huxley in 1874, Langerhans in 1876, Lankester in 



