ALIMENTARY CANAL 



13 



connected at intervals by chitinous " synapticula " (Fig. 5, s), 

 which traverse one or the other of the halves of the gill-slit. ' In 

 Dolichofflossus, where no synapticula occur, the tongue-bars may 

 be turned inside out by slight pressure, and then project to the 

 exterior through the gill-pores. 



The subdivision of the branchial region of the alimentary 

 canal into two parts, as shown in Fig. 4, is characteristic of 

 Glossobalanus and its allies. In Dolichoglossus and Glctndiceps 

 there is no such constriction, the region occupied by the gill-slits 

 being merely the dorsal half of a tube with a simple circular 

 section. Schizocardium (Fig. 

 6) agrees with Amphioxus 

 in the fact that the gill-slits 

 occupy nearly the whole of 

 the wall of the pharynx ; 

 the only parts not perfor- 

 ated by gill-slits being the 

 small dorsal and ventral 

 portions. 



In Ptychodera (Fig. 4), 

 the gill-sacs are practically 

 absent. The U-shaped slits 

 of the pharyngeal wall thus 

 open directly to the exterior,^ 

 and can be seen from the 

 outside. In species which 

 have this arrangement, the 

 genital wings are greatly 

 developed, so as to arch over 

 the back of the branchial 

 region. The gill-slits thus 

 open into a kind of " atrium," resembling that of Amphioxus 

 in its relation to the gill-slits, and in having the generative 

 organs on its outer side, but differing from it in being dorsal to 

 the pharynx. 



At a certain distance behind the branchial region, the 

 alimentary canal in Balanoglossus and Schizocardium is produced 

 into a series of outgrowths, into which food does not pass. 

 These "liver-sacs'' give rise to corresponding folds (Fig. 1, A, A) 



1 Spengel, Monogr. pp. 179, 187 ; Willey, Zool. Res. iii. p. 236. 



Fig. 6. — Schizocardium hrasiliense ; transverse 

 section through the branchial region, show- 

 ing tlie great extent of the branchial part 

 (h) of the pharynx ; the oesophageal part 

 (o) is reduced to a mere groove ; (7, gill- 

 pore ; ^.5, gill-sac ; r, reproductive organ ; 

 s, synapticula (cf. Fig, 5) ; t, tongue-bar. 

 The muscles of the body-wall are not indi- 

 cated : in other respects the figure corre- 

 sponds with Fig. 4, except for the absence 

 of genital wings in this region of the body. 

 (After Spengel.) 



