CHORDATA 



211 



double row of ovaries or testes, are extruded through pores in the 

 body wall. (Figure 98.) 



Some species of Balanoglossidae have a ciliated larva called the 

 Tornaria, which was once considered a larval Rchinoderm. (See p. 

 217.) Cephalodiscus and Rhadopleura are colonial Hemichorda, 

 which reproduce by buds. Both these forms were at one time re- 

 garded as Polyzoa. They have small probosces, and their alimen- 

 tary canals are bent. Both are deep-sea forms. 



Subphylum Urochorda. (Tunicates, Sea Squirts, Ascidians.) 

 Characteristics. — i. Retrogressive metamorphosis. 



2. Multiplication by budding, as well as by gonads. 



3. Reversal of the heart beat. 



4. A tunic or mantle composed of cellulose (CeHioOs). 



Adult sea squirts (Figure 99, A, B, C, D, E, F) resemble the 

 siphonate molluscs in the possession of incurrent and excurrent ori- 

 fices and a mantle. The Tunicates hence were long associated with 



Molgula 

 manhattensis 



Molgula 

 arenata 



Eugyra 

 pillularis 



Botryllua 

 gouldii 



Cynthia partita 



Salpa cabotii 



Fig. 99. A group of Urochorda. J, Molgula manhattensis. B, Molgula arenata. 

 C, Eugyra pillularis. D, Cynthia partita. E, Botryllus gouldii. F, Salpa Cabotii. 

 (From Verrill.) 



