I IO 



ACIPENSER. 



As the posterior part of the 

 trunk, containing the intestine, 

 becomes formed, the yolk is 

 gradually confined to the an- 

 terior part of the alimentary 

 tract, which, as before stated, 

 becomes the stomach. The 

 epithelial cells of the stomach, 

 as well as those of the intestine, 

 are enormously dilated with 

 food-yolk (fig. 57, st). Behind 

 the stomach is formed the liver. 

 The subintestinal vein bring- 

 ing back the blood to the liver 

 appears to have the same course 

 as in Teleostei, in that the 

 blood, after passing through 

 the liver, is distributed to the 

 walls of the stomach and is 

 again collected into a venous 

 trunk which falls into the sinus 

 venosus. As the yolk becomes 

 absorbed, the liver grows for- 

 wards underneath the stomach 

 till it comes in close contact 

 with the heart, 

 position of the 

 is shewn 



Cto 



The relative 

 parts at this 



stage 



diagrammati- 



FIG. 57. TRANSVERSE SECTION THROUGH 

 THE REGION OF THE STOMACH OF A LARVA OF 

 ACIPENSER 5 MM. IN LENGTH. 



s/. epithelium of stomach ; yk. yolk ; ch. 

 notochord, below which is a subnotochordal 

 rod ; pr.n. pronephros ; ao. aorta; mp. muscle- 

 plate formed of large cells, the outer parts of 

 which are differentiated into contractile fibres ; 

 sp.c. spinal cord ; b.c. body cavity, 

 cally in fig. 56. At the com- 

 mencement of the intestine there arises in the larva of about 14 mm. a 

 great number of diverticula, which are destined to form the compact 

 glandular organ, which opens at this spot in the adult At this stage 

 there is also a fairly well developed pancreas opening into the duodenum 

 at the same level as the liver. 



No trace of the air-bladder was present at the stage in question. 

 The spiral valve is formed, as in Elasmobranchii, as a simple fold in the 

 wall of the intestine. 



There is a well developed subnotochordal rod (fig. 57) which, according 

 to Salensky, becomes the subvertebral ligament of the adult ; a statement 

 which confirms an earlier suggestion of Bridge. The pronephros (head- 

 kidney) resembles in the main that of Teleostei (fig. 57) ; while the front 

 end of the mesonephros, which is developed considerably later than the 

 pronephros, is placed some way behind it. In my oldest larva (14 mm.) 

 the mesonephros did not extend backwards into the posterior part of the 

 abdominal cavity. 



