17 



iituri'. The Hccomiunvin^ illustration i Fi U '. Hi will serve to impress the 

 mutter. 



Tin- discipline in tin- nutrithe processes requin-s the blood to be brought 

 from tlie vitellus and a rated in the allantois. thence to be dispatched through 

 the Imdy territories. Accordingly tun great venous trunks (omplialo-meseraic 

 veins i, one in each fold of the aplanahnopfetm, embnofng the vitellus, are the 



KI<;. s. MuiiRAM OK l-ntti.'- Koa. A, yelk; '. vitel!im> membrane; c, chnlaziferous membrane; 

 d, albumen; e. f. miililli* anil internal shell memiirane.-i : y, uir chamber; A, calcareous shell. 

 (Aftr Dalton.) 



first evolved, while at the terminal ends or confluence the heart is formed by the 

 blending of the walls of these venous trunks. 



According to His. the heart is developed by the coalescence of a layer of the 

 splauchnopleure with a similar layer from the somatopleure, the hollow cavity 

 formed by the union bein^ in free communication with the adjacent omphalo- 



FIC. !). Eoo or FOWL is I 'HOC BSD 

 circulation, terminal sinus, etc. 



[)KVKt.opjiEXT, showing area vasculo.ia. with vitelllne 



meseraic veins. According to Foster and Balfour " the upper end of the heart 

 is developed out of the mesoblast of the splanchnopieure," but " increases in 

 length step by step at the expense of the continually coalescing ouiphalo- 



