368 TEXTBOOK OF ZOOLOGY 



respectable ehordate to become a lazy, stationary form which is not 

 much more than a water-bag whose level of development has degen- 

 erated almost to that of a sponge. Certain of the sessile forms, which 

 reproduce also by budding, develop colonies with a common tunic. 

 This form is one of the few colonial ehordate animals. In a few 

 instances tunicates reproduce one generatioji 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 : Bra7ichiostoma virginiae, B. floridae, B. lermu- 

 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 

 average 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 a ehordate, possessing only rare 

 essentials. It is usually referred to as a close ancestral relative of 

 Vertebrata. 



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

 of the subtropical and tropical portions of the world. These ani- 

 mals 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 Mediter- 

 ranean 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, particu- 

 larly 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 



