248 PROFESSOR HUXLEY ON THE ANATOMY 



EXPIANATION OE THE PLATES. 

 Plates XXX. and XXXI. 



The following letters and figures have the same signification throughout. 



a, the test; a', its oral; or, its eloacal fibrillated layer; a^, labial processes of the ascidiozooids ; «*, lip or 



so-called sphincter of the eloacal aperture ; w', cells of the embryonic test. 



b, outer tunic. 



c, inner tunic, or intestinal wall. 



d, atrial tunic. 



e, oral aperture. 



/, tentacular membrane ;/', haemal tentacle. 

 g, g I .anterior muscles ; g^, posterior or atrial muscles. 

 h, peripharyngeal ridge. 

 i, endostyle. 

 j, epipharyngeal folds. 



k, hypopharyngeal band and sinus ; k\ languets ; h, diapharyngeal band. 

 I, branchial sac; U, horizontal bi'anchial bars; P, perpendicular branchial bars; P, stigmata, 

 m, alimentary canal ; »»', oesophageal aperture ; m^, oesophagus ; m^, stomach ; m'*, intestine. 

 n, tubular organ, probably hepatic. 



0, anus. 



p, mid-atrium ; p^, lateral atria ; p^, atrial aperture. 



r, heart ; r', sinuses ; r'^, stolons of the adult ascidiarium ; r^, vascular bands, connecting the branchial 



sac with the parietal sinus ; r*, stolons of the embryonic ascidiarium, or tetrazooid. 

 s, ovisac ; s', its duct ; s^, lining of the ovisac. 

 t, testis ; /', vas deferens ; f, spermatozoa. 



M, yelk ; m', germinal vesicle ; u^, germinal spot ; m^, contents of the germinal vesicle. 

 w, bud ; w', its peduncle. 

 X, alimentary or trophic blastema of the nascent bud; ^', its generative blastema; x^, its tegumentary 



blastema. 

 y, the circular cellular patch, probably a renal organ. 

 z, the ganglion ; z^, nerves ; z'^, the ciliated sac ; z^, the tubercle. 

 ce, elaeoblast. 



en, embryonic endoplasts within the germinal vesicle. ^ 



bl, blastoderm. 

 cl, cloaca, - I 



I. II. III. IV. V. Segments of the blastoderm, i. Cyathozooid. ii.-v. Ascidiozooids. 



1, 2, .3, 4, isthmuses. 



y8, the mouth of the cyathozooid, as formed by the test, and which becomes the future lip or ' sphincter' 

 of the eloacal aperture; /3', aperture of the cyathozooid when separated from the foregoing. 



7, cavity of the cyathozooid. 



8, appendix of the cyathozooid. 

 6, canal connecting the first isthmus with the cavity of the cyathozooid. 



