ANATOMY AND DEVELOPMENT. 



189 



a duct which runs forward and opens at the end of a 



ciUated funnel-shaped dilatation into the branchial sac at 



the base of the buccal tube 



(Figs. 94, 96, and 97) in 



front of the peripharyngeal 



band. 



The branchial opening of 

 the duct of the subneural 

 gland appears primarily as 

 a simple circular orifice, but 

 it does not usually retain 

 this character in the adult. 



Generally it assumes a 

 crescentic form by the in- 

 curving of its anterior or 

 posterior lip, and then in 

 many cases the horns of the 

 crescent so formed become 

 coiled over and over con- 

 centrically, and usually in 

 approximately the same 

 plane, so that the lips of 

 the aperture assume a very 

 complicated appearance and 

 constitute the so-called dor- 

 sal tubercle (Fig. 97). 



It has taken a long time 

 and the work of a great 

 many zoologists to achieve 

 our present knowledge 

 (which is by no means 

 complete) of the subneural gland of Ascidians and its 

 duct. 



Fig. 96. — Young Clavelina, shortly 

 after tlie metamorphosis, from the right 

 side. (After VAN Beneden and JULIN.) 



at. Atrial opening, at.c. Atrial cav- 

 ity, b.s. Blood-sinus. end. Endostyle. 

 ep. Epicardium ; outgrowth from bran- 

 chial sac behind endostyle, which grows 

 down into the creeping stolon, forming 

 a septum in the latter, and being the 

 chief element in the production of buds. 

 f. Lobes of the fixing organ, which give 

 rise to the creeping stolon, g. Ganglion. 

 g.s. Stigmata, h. Heart, liy. Hypophysis 

 (dorsal tubercle). int. Intestine. m. 

 Mouth, oes. QEsophagus. p.b. Periphar- 

 yngeal band. pc. Pericardium, t. Re- 

 mains of tail, withdrawn into the body. 

 v.n. Visceral nerve. 



