TIM ORGANS 01 I in: MIDDLE GERM I.A\KK. 



3G5 



similar structure > oi the e.vn-iMi-v < L r ment-d Worms. In 



the most of the Vertebrate.-, however, special m-jliri.li;il funnel- an- 

 no Ion- i -1 A eloped, inasmuch a- (he in- >onephric tulniles soon after 

 I heir origin completely detach themselvo I'mm the epithelium of tin- 

 i odv cavitv a> well a- tVin the primit i\ < 

 L6nt8 and therehv IM-C nil relation to 

 (lie body cavity. 



A mesonephros in the simple form in 

 \vhicli it i> at tii->! jinulncrl develop- 

 inentalls i> retained }iermanently only 

 in Jldello-toina. a rej>re-entat ive of the 

 ( 'yelo>tomes. It here i'ini.si^t>, as Jo- 

 IIANNKS Ml' 1. 1. Kit h:^ >ll<>\\ 11, of Ull eloll- 



gated canal (fig. 206 A and B a) and 



short tran-ver>e tnhides (f>), which open 

 into it at short intervals. The latter are 

 no longer connected with the body-cavity 

 ly mean> of a nephridial funnel, but they 

 enclose a vascular ^lomcrulus at their 

 l)lind end (fig. 206 B c), which is some- 

 what set off by a constriction. 



In all remaining AVrtehrates the meso- 

 nephros i- metamorphosed into a more 

 voluminous and more complicated orpin. 

 I -'or the originally short tubules, which 

 run traiisveiM-ly into the mesonephric 

 duct, begin to grow in length, and at the 

 same time to be thrown into nuiiienni- 

 folds (fi<:. L'07 *.('). Moreover there are 

 formed mesonephric tubules of a second 

 and third order. These again are also 

 formed independently of the mesonephric 

 duct dorsal to the lirst -formed transverse 

 tuhules; their blind ends approach the 

 primary urinary tubule and join its ter- 

 minal part, which i- thereby converted 



into a collecting tube. At the same time a .Malpighian body is 

 loimed on each of tl,. m I 



still more exhaustive h.\ s concerning the formation of the second 



:iry and tertiary inoui,. i-liric tubules, especially for the higher Vertebrates. 

 pjx ai to me to be desiiabU-. In the Sel;! the statements 



Fig. 206. Parts of the mesone- 



phros of Myxine. nf 



Mri.i i i:. 

 a, Mesonephric duct ; 6, mesone- 



HHH tuhules; c, glomeriilus ; 



<^, afferent artery ; e, t !' 



artery. 



it of A more highly mag- 



