EMBRYOLOGY OF TADPOLE AND CHICK 



545 



Order 2. Pterobranchiata, sessile, tube-dwelling forms Cephalo- 



discus and Rhabdopleura. 



Order 3. Phoronidia, tubicolous forms Phoronis (Fig. 199). 

 Sub-Phylum IV. Vertebrata (Craniata). 



v. 



VI. 



VII. VIII. 



Fig. 313. 



V. Botryllus violaceus. 



VI. Composite Ascidian. 'Diagram of an individual member of a colony of 

 composite Ascidians. The zooids are in pairs and seen in vertical section, an, 

 anus; at, atrium; at', atrium of adjoining zooid ; cl, cloaca common to both 

 zooids ; end, endostyle ; gld, digestive gland ; gn, nerve ganglion ; ht, heart ; hyp, 

 neural gland ; lang, languets ; mant, mantle ; or.ap, oral aperture ; ov, ovary ; 

 periph, peripharyngeal band ; ph, pharynx ; reet, rectum ; stom, stomach ; te, testis ; 

 tent, tentacles ; tst, test or common gelatinous mass in which individuals are im- 

 bedded ; v.d, vas deferens ( V, after Mile-Edwards ; VI, after Herdman. ) 



VII. Salpa democratica, asexual form, ventral view, and VIII lateral view in 

 section, at, atrial cavity ; atr.ap, atrial aperture ; br, branchia ; branch, dorsal 

 lamina ; c.c, ciliated crests on edge of branchia ; c.f, ciliated funnel ; d.l, dorsal 

 lip ; end, endostyle ; ey, eye ; gl, digestive gland ; gn, ganglion ; ht, heart ; int, 

 intestine ; Ing, languet ; mo, mouth ; mus.bds, muscular bands ; ne.gn, nerve- 

 ganglion ; 02, oesophagus ; oe.ap, and or.ap, apertures of oesophagus and mouth ; 

 ph, pharynx ; pp, peripharyngeal band ; proc, processes at posterior end ; sens.org, 

 sensory organ ; st, and stol, stolon ; st, on left, stomach ; v.l, ventral lip. ( VII, 

 after Vogt and Jung, VIII, after Delage and Herouard.) 



Order 1. Cyclostomata (round mouth eels), such as hagfish and 



Lampreys (Fig. 312). 

 Order 2. Pisces (true fish with jaws). 



