CHAPTER IV 
CEPHALOCHORDATA 
INTRODUCTION——GENERAL CHARACTERS—-ANATOMY OF AMPHIOXUS 
—EMBRYOLOGY AND _ LIFE-HISTORY——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 Lranchiostoma 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 Branchiostoma, by Costa, in 1834. The term 
Amphiozus, 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 
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