PHYLUM CHORDATA 



393 



group are either free-swimming or fixed, colonial or solitary. 

 The colonial forms reproduce asexually by budding, as well as 

 sexually. Examples : 

 Ciona (Fig. 338), Cyn- 

 thia, Molgula, Botryllus, 

 Pyrosoma. 



Order 2. Thaliacea 

 (Fig. 337, central por- 

 tion). — These are free- 

 swimming, solitary, or 

 colonial forms living near 

 the surface of the sea, 

 i.e. pelagic. The com- 

 monest genus, Sal pa 

 (Fig. 340, A), is cylin- 

 drical, and its hoop-like 

 muscle bands cause it to 

 resemble a barrel. Usu- 

 ally there is an alterna- 

 tion of generations ; a 



B 



Fig. 340. — A, a solitary Tunicate, Salpa 

 democratica, dorsal view. /, muscle bands; 

 2, " gill " ; j, endostyle; 4, peripharyngeal 

 band; 5, brain; 6, ciliated pit; 8," nucleus " 

 of stomach, liver, intestine; q, stolon; 10, pro- 

 cess of mantle; 11, mouth. (From Shipley 

 solitary individual gives and MacBride, after Brooks.) B, Oiko pleura 



cophocerca in its test. (From Sedgwick's 

 Zoology, after Fol.) 



rise asexually to a row of 



sexual members, each of 



which produces a single egg; the eggs develop into asexual 



solitary individuals. 



Order 3. Larvacea (Fig. 337, upper portion). — The Lar- 

 vacea are small pelagic forms which retain the larval condition 

 throughout life. Examples: Appendicular la, Oikopleura (Fig. 

 340, B). 



3. SUBPHYLUM III. CEPHALOCORDA 



This subphylum contains about a dozen species of marine 

 animals of which Branchiostoma lanceolatus, commonly known as 

 Amphioxus or the Lancelet, is the form usually studied. Am- 

 phioxus is of special interest, since it exhibits the characteristics 



