GANOIDEI. 



side of the insertion of the mesentery, and extending upwards 

 and outwards round the segmental duct 1 . The posterior seg- 

 mental tubes arise later than the anterior, and (as far as can be 

 determined from the sections in my possession) they are formed 

 independently of the peritoneal epithelium, on the dorsal side 

 of the segmental duct. 



In later stages (larvae of 7 10 mm.) the anterior segmental 

 tubes gradually lose their attachment to the peritoneal epi- 

 thelium. The extremity near the peritoneal epithelium forms a 

 Malpighian body, and the other end unites with the segmental 

 duct. At a still later stage wide peritoneal funnels are es- 



sp.c 



pr.n 



FIG. 398. TRANSVERSE SECTION THROUGH THE REGION OF THE STOMACH OF A 



LARVA OF ACIPENSER 5 MM. IN LENGTH. 



st. epithelium of stomach ; yk. yolk ; ch. notochord, below which is a subnoto- 

 chordal 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. 



tablished, for at any rate a considerable number of the tubes, 

 leading from the body cavity to the Malpighian bodies. These 



Whether the segmental tubes are formed as ingrowths of the peritoneal 

 epithelium, or in situ, could not be determined. 



