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LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



functional cases. The glomeruli of the pronephros are generally of the type known as external 

 glomeruli, that is, they project into the coelom adjacent to the nephrostome and are not directly 

 associated with the tubule (Fig. 61). In some cases, however, internal glomeruli which project 

 into the tubule occur. 



B 



FIG. 60. Diagrams to show the development of the three kidneys and their ducts and their 

 relation to the male gonad. A, early stage showing the pronephros a developing from the anterior end 

 of the mesomere c and the pronephric duct b which has not yet reached the cloaca e. B, next stage, 

 illustrating the degeneration of the pronephros at /, the development of the mesonephros h from the 

 middle portion of the mesomere, the junction of the pronephric duct, now the mesonephric duct g, 

 with the cloaca and the beginning of the metanephric evagination i from the mesonephric duct. C, later 

 stage, showing connection between certain tubules of the mesonephros and the testis j by means of 

 tubules, the vasa efferentia p, which grow out from the mesonephros; and the penetration of the meta- 

 nephric evagination into the posterior end of the mesomere where it is subdividing to form the collecting 

 apparatus /, which becomes associated with secretory metanephric tubules m, developed in the meso- 

 mere. D, final stage, in which the mesonephros has disappeared except for the remnant q which con- 

 nects with the testis j by means of the vasa efferentia p; the mesonephric duct g persists as the vas 

 deferens; the two parts of the metanephros shown hi C have united to form a single organ r. a, pro- 

 nephros; b, pronephric duct; c, mesomere or nephrotome; d, intestine; e, cloaca; /, degenerating 

 pronephros; g, mesonephric or Wolffian duct; h, mesonephros or Wolffian body; i, metanephric evagina- 

 tion from the Wolffian duct in B, ureter in C and D; j, testis; k, coiled portion of the vas deferens form- 

 ing part of the epididymis; /, collecting part of the metanephros derived from the Wolffian duct; m, 

 execretory tubules of the metanephros derived from the mesomere; n, nephrostome; 0, renal corpuscle 

 or Malpighian body; p, vasa efferentia; q, remnant of the mesonephros, forming part of the epididymis; 

 r, metanephros. 



6) Mesonephros: The second vertebrate kidneys are the paired mesonephroi (singular, 

 mesonephros), also known as the Wolffian bodies, after the embryologist Wolff, who first 



