424 THE ORIGIN OF VERTEBRATES 



called suprarenal ; a segmental series of paired organs, each of which 

 possesses a branch from the aorta and a sympathetic ganglion, and an 

 unpaired series in close connection with the kidneys, to which Balfour 

 gave the name of interrenal glands. Of these two sets of glands, 

 Swale Vincent has shown that the extract of the interrenals has no 

 marked physiological effect, in this respect resembling the extract of 

 the cortical part of the mammalian gland, while the extract of the 

 paired segmental organs of the Elasmobranch produces the same 

 remarkable rise of blood- pressure as the extract of the medullary 

 portion of the mammalian gland. 



The development also of these two sets of glands is asserted to be 

 different. Balfour considered that the suprarenals were derived from 

 sympathetic ganglion-cells, but left the origin of the interrenals 

 doubtful. Weldon showed that the cortical part of the suprarenals 

 in the lizard was derived from the wall of the glomerulus of a 

 number of mesonephric tubules. In Pristiurus, he stated that the 

 mesoblastic rudiment described by Balfour as giving origin to the 

 interrenals is derived from a diverticulum of each segmental tubule, 

 close to the narrowing of its funnel-shaped opening into the body- 

 cavity. With respect to the paired suprarenals he was unable to 

 speak positively, but doubted whether they were derived entirely 

 from sympathetic ganglia. 



Weldon sums up the results of his observations by saying : 

 " That all vertebrates except Amphioxus have a portion of the 

 kidney modified for some unknown purpose not connected with 

 excretion ; that in Cyclostomes the pronephros alone is so modified, 

 in Teleostei the pro- and part of the meso-nephros ; while in the 

 Elasmobranchs and the higher vertebrates the mesonephros alone 

 gives rise to this organ, which has also in these forms acquired a 

 secondary connection with certain of the sympathetic ganglia." 



Since Weldon's paper, a large amount of literature on the origin 

 of the adrenals has appeared, a summary of which, up to 1891, is 

 given by Hans Eabl in his paper, and a further summary by Aichel 

 in his paper published in 1900. The result of the investigations up 

 to this latter paper may be summed up by saying that the adrenals, 

 using this term to include all these organs of whatever kind, are in 

 all cases, partly at all events, derived from some part of the walls of 

 either the mesonephric or pronephric excretory organs, but that in 

 addition a separate origin from the sympathetic nervous system must 



