72 



CHORDATE ANATOMY 



The adult kidney (Fig. 271) consists of the entire system of tubules — 

 mesonephric or metanephric — of one side of the embryo, increased to 

 great number by formation of secondary tubules from the primary tubules, 

 each tubule tremendously elongated and much coiled, the tubules bound 

 together by connective tissue with blood-vessels richly interspersed, 

 and the whole complex ensheathed by connective tissue and thereby 

 delimited from adjacent tissues of the body-wall. 



The hypomere mesoderm, later backed up by a layer of connective 

 tissue, becomes the definitive peritoneum. Its somatic layer completely 



MVJ 



Fig. 65. — Diagrammatic transverse section of the body of a vertebrate showing 

 relations of organs to the peritoneum and coelom. A, dorsal aorta; C, coelom; EN, 

 endodermal epithelium of digestive tube; G, gonad; /, integument; K, kidney ;L, liver; 

 M, musclelayer of digestive tube; MD, dorsal muscle of body-wall; MV, ventral muscle 

 of body-wall; NC, position of embryonic notochord; NT, neural tube (spinal cord); 

 PP, parietal peritoneum; PV, visceral peritoneum; R, rib; VC, vertebral column. 



lines the body-wall. Its visceral layer covers the coelomic surfaces of the 

 digestive tube and of all other organs which occupy the coelom. In 

 the median plane at all regions not occupied by median organs (Fig. 58) 

 the right and left visceral layers of the hypomere meet one another to 

 coalesce and become membranes or mesenteries which connect and support 

 the viscera. In later stages of development the mesenteries undergo 

 considerable reduction, especially those between the digestive tube and 

 the ventral body wall (Fig. 60). Figure 65 shows the ideal relations of 



