544 



THE EMBRYOLOGY OF THE FROG 



Sub-Phylum II. Urochordata (Figs. 312, 313). 



Order 1. Larvacea (Appendicularia), free-swimming forms with 

 permanent tail. 



Order 2. Ascidiacea (Tunicates or Sea-Squirts), fixed forms with- 

 out tail in the adult. 



Order 3. Thaliacea (Salpians), free-swimming forms without tail 

 in the adult. 



ii. 





III. IV. 



Fig. 313. 

 UROCHORDATA. 



I. Oikopleura in 'house'. The arrow shows course of current. 



II. Diagram of Appendicularia from the right side, an, anus ; ht, heart ; int, 

 intestine, ne, nerve; ne' , caudal portion of nerve; ne.gn' , principal nerve 

 ganglion; ne.gn"., ne.gn"'., first two ganglia of tail nerve; noto., notochord ; 

 oes., oesophagus; or.ap., oral aperture; oto. otocyst (statocyst) ; peri.bd., peri- 

 pharyngeal band ; ph., pharynx ; tes., testis ; stig., one of the stigmata ; stom. 

 stomach. (After Herdman. ) 



III. and IV. Ascidia. Entire animal as seen from the right side and dissection 

 from the same side, an, anus ; atr.ap, atrial aperture ; end, endostyle ; gon, gonad ; 

 gonad, gonoduct ; hyp, neural gland ; hyp.d, duct of neural gland ; mant, mantle ; 

 ne.gn. nerve-ganglion ; oes ap, aperture of oesophagus ; or ap, oral aperture ; 

 ph, pharynx; stom, stomach; tent, tenacles ; test, testes. (After Herdman.) 



Sub-Phylum III. Hemichordata (Fig. 314). 



Order 1. Enteropneusta, including worm-like forms such as Balano- 

 glossus. 



