. The Cambridge natural history. Zoology. 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 occup
. The Cambridge natural history. Zoology. 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. 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- po
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
