284 



CEPHALOPODA. 



a. 



Various prominences and folds appear in the epithelium of the stomodaeum 

 near the mouth, and the jaws also arise here as cuticular secretions (JouBiN, 

 GBENACHER, BOBBETZKY). 



Long before the differentiation of the stomodaeum advanced to this 

 point, it became united to the rudiment of the enteron, the two having 

 grown up towards each other from opposite sides of the yolk, and 

 having met near the apex of the inner yolk-sac, there fusing. Fig. 

 133 represents a later stage, in] which the enteron has dilated 

 anteriorly and has thus formed the rudiments of the stomach (mg) 

 and of the stomach-caecum (&>). 



At a somewhat earlier stage, the rudiment of the enteron shows a 



remarkable peculiarity, 

 being wide open to- 

 wards the yolk-epi- 

 thelium, as is evident 

 in sagittal sections 

 (Fig. 132 0) and still 

 more in transverse 

 sections (Fig. 134 A 

 and ft). It here 

 appears as a plate, &. 

 large part of which is 

 in close contiguity to 

 the yolk. The in- 

 folding of the edges of 

 this plate (Fig. 134 E) 



""" '^'^ ""^ReS^ 



fc. 



FIG. 134. The ventral portions of two transverse sec- 

 tions of embryos of Loligo mdgaris at different ages 

 (original), a, anal region ; de, yolk-epithelium ; 

 ect, ectoderm ; k, branchial rudiments ; I, liver ; md, 

 enteron ; mes, mesoderm ; v, vascular spaces in the 

 mesoderm. 



gives rise to the two 

 hepatic tubes which 

 open into the enteron 

 in the region of the 

 caecum. 



The wide opening 



of the enteron towards the yolk-epithelium gradually narrows, 

 but can still be distinctly made out even in later stages (Fig, 

 133). Below it, large cells of the yolk-epithelium can be se"en 

 lying, and sending off lateral processes into the yolk (Fig. 133). 

 The yolk is thus completely covered by the yolk-epithelium even 

 beneath these gaps in the intestinal epithelium, where a con- 

 nection of the lumen of the intestine with the yolk-sac might be 

 assumed, as well as below the former wide aperture of the enteron. 

 There is, therefore, no direct communication between yolk-sac and enteron* 



