. Text-book of embryology. Embryology. 364 INVEETEBEATA CHAP. pnf ventral diverticula grow out, whicli are the rudiments of the salivary glands. The mid-gut becomes differentiated into a stomach and an intestine, and the diverticulum which forms the ink sac opens into the latter. The liver arises as two lateral outgrowths of the stomach. The surfaces of these outgrowths become folded, and this is the first indication of the formation of the liver tubules. The coelom, which is already constricted into kidney and pericar- dium, now increases greatly in volume. The two pericardial rudiments fuse
. Text-book of embryology. Embryology. 364 INVEETEBEATA CHAP. pnf ventral diverticula grow out, whicli are the rudiments of the salivary glands. The mid-gut becomes differentiated into a stomach and an intestine, and the diverticulum which forms the ink sac opens into the latter. The liver arises as two lateral outgrowths of the stomach. The surfaces of these outgrowths become folded, and this is the first indication of the formation of the liver tubules. The coelom, which is already constricted into kidney and pericar- dium, now increases greatly in volume. The two pericardial rudiments fuse behind and enclose the two rudiments of the heart; these latter likewise fuse together. In front the pericardial rudi- ments remain separate and are applied to the paired rudiments of the heart which here con- stitute the auricles. The paired portions of the pericardium communicate with the kidneys and give rise to the reno- pericardial canals. Behind, the single pericardium grows backward and extends into the growing genital organ, which becomes divided up into the genital folds. This portion of the pericardium becomes, later, divided off from that sur- rounding the heart and forms the genital coelom (Fig. 297). The kidney sacs develop a high columnar epithelium on their inner walls, where they are in contact with the forlcs of the vena cava; the epithelium lining their outer walls becomes very thin. The posterior sinus is reduced to very small dimensions by the expansion of the shell-sac, and is cut off from the vena cava. The portions of the vena cava which extend into the gills and constitute the branchial hearts, develop great thickenings of their walls on one side. These thickenings, as experiment has proved, are excretory in nature and consist of vacuolated cells ; they are covered externally by thin peritoneal epithelium where they touch the coelom. These are of course the appendages of the branchial heart. The cartilage so characteristic of Cephalopoda is formed by the
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Keywords: ., bookcentury1900, bookdecade1910, bookpubli, booksubjectembryology
