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 : 

 dona (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, Salpa 

 (Fig. 340, A), is cylin- 

 drical, and its hoop-like 

 muscle bands cause it to FIG. 340. A, a solitary Tunicate, Salpa 

 resemble a barrel. Usu- democratica, dorsal view. /, muscle bands; 



2, gill ; 3, endostyle; 4, penpharyngeal 



ally there is an alterna- band; 5, brain; 6, ciliated pit; 8, "nucleus" 

 tion Of generations; a of stomach, liver, intestine; 9 , stolon; /o pro- 



cess of mantle; //, mouth. (From Shipley 



Solitary individual gives and MacBride, after Brooks.) B, Oikopleura 

 rise asexually to a row of ^phocerca in its test. (From Sedgwick's 

 * Zoology, alter rol.) 



sexual members, each of 



which produces a single egg; the eggs develop into asexual 



solitary individuals. 



Order 3. Larva'cea (Fig. 337, upper portion). The LAR- 

 VACEA are small pelagic forms which retain the larval condition 

 throughout life. Examples: Appendicularia, 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 



