152 ESSENTIALS OF ZOOLOGY 



*'chin. " It now undergoes regressive changes involving loss of tail, 

 notochord, and posterior portion of nerve cord. The anterior por- 

 tion of the cord becomes a simple ganglion. The paired eyes and 

 otocysts (ear structures) also disappear. This process of meta- 

 morphosis has caused an active respectable chordate to become a 

 lazy, stationary form which is not much more than a water-bag 

 whose level of development has degenerated almost to that of a 

 sponge. In a few instances tunicates reproduce one generation 

 sexually, and the next is produced by budding (asexually). This 

 alternation of generation is another retrogressive feature. 



Subphylum Cephalochorda, Amphioxus 



There are usually listed twenty-eight species in this group which 

 are rather locally distributed over the world. There are four species 

 on American shores : Branchiostoma virginiae, B. floridae, B. hermu- 

 dae, and B. calif orniense. Amphioxus or the lancelet, Branchiostoma 

 lanceolatus, the European form, is an admirable representative of 

 the subphylum and has become classical in its use. However, it is 

 likely that B. virginiae or B. floridae is more commonly studied in 

 the United States. It is a small, fishlike, marine animal whose aver- 

 age adult length is about two or three inches. In its adult form it 

 represents clearly the distinctive characteristics of the phylum in a 

 simple condition. It is usually referred to as a close ancestral rela- 

 tive of the Vertebrata. 



Habitat. — It is found in shore water and on the sandy beaches of 

 the subtropical and tropical portions of the world. These animals 

 are found along our Atlantic Coast as far north as Chesapeake Bay, 

 at certain points in the Gulf of Mexico, and on the southern Pacific 

 Coast. They may be found along the shores of the Mediterranean 

 Sea, the Indian Ocean, and along the southern coasts of China. 



Habits and Behavior. — It burrows rapidly, head first, in the sand 

 by means of a vibratory action of the entire body, but comes to 

 rest with the anterior end exposed to the water. At' times, partic- 

 ularly at night and during breeding season, the animal leaves the 

 burrow and swims about like a fish by means of lateral strokes of 

 the posterior portion of the body. 



External Structure. — The body of this animal is shaped like a 

 small lance, the tail being the point. In general, it is similar to 

 a small fish, but it does not have a distinct head. The mouth opens 



