i in: MIMM. i-; Q1B1I 407 



undilltMvntiated e.-11-mass (the middle plate Of 'In- m.--.n,.phnc 

 blastema), out of which (lie mcsonephric tuhules subsequently 

 \\l,en they l>ecome clearly dist in^ui.-habl'- bo have been 



differentia 



15. Jn a part of (In- nmt-ainniot ic Vertebrates (some Selaeln 

 Amphibians) tin- pi iinit ive kidney n-mains in open communieat ion 

 with (lie ho.ly-cavity hy means < f numerous riliate fimne's mephro- 

 stomes), whereas in all Amn : .,!;i i he me-onephric, tulmles early 

 surrender their genetically e-t iMi-lied emmet-i i >n with tlio loly- 

 eavity through the disappearance of the cili it<- t'unnel>. 



16. The permanent kidney (metanephroe) is the latest to be 

 formed and takes its origin from two separate j-aits : 



(a) From an t-va^ination of the end of (lie inesonephric duct, 



which furnishes the ureters, the pelvis of the kidney, and 

 the straight urinary tubules (in other words, the efferent 

 apparatus) ; 



(b) l-'rom a renal blastema, which represents a backward pro- 



longation of the mesonephric blastema, has the -auie 

 origin as the latter, and is converted into the tortuous 

 urinary tubules with the Malpighiau corpuscles (therefore 

 the secretory part of the kidney). 



17. The fundaments of the kidney, which have arisen far luck in 

 the body, rapidly increase in M/.e and undergo a change of position 

 by moving farther forward by the side of the primitive kidneys, 

 whereby the ureter becomes wholly detached from the mesonephric 

 duct and moves to the posterior [dorsal] surface of the allantois, the 

 future urinary bladder. 



18. In the non-amniotic Vertebrates the mesonephros also gives 

 rise by a process of fission to the Miillerian duct, which runs 

 parall 1 with it. 



19. In the Amniota the relation of the Miillerian duct to the 

 nephric duct is still uncertain, because the front end of the former 



is established by a groove-like depression of the epithelial invest- 

 ment on the lateral face of the me>onephivs, while coiu-erning the 

 remaining part it is still undetermined \\hotherit grows backwards 

 independently or is constricted oft' from the mesonephric duct. 



20. The sexual glands proceed from two fundaments : 



(u) From a germinal pit helium, a modified part of the epithelium 

 of the body-cavity, located on the median face of the 

 primitive kidney ; 



(b) From the sexual cords, which grow cut toward the germinal 



