NEPHRIDIA OF CERTAIN EARTHWORMS. 403 



that the external apertures do not each correspond to a 

 nephridium isolated from its fellows ; the nephridial tufts form 

 a continuous layer coating the body wall; there must therefore 

 be a network, although it may not be of course so complete a 

 network as I have sketched in the figure just referred to. 



Typhseus, F. E. B., and Dichogaster, n. g. 



I have observed numerous nephridiopores in a single seg- 

 ment in both these genera ; at present I can only record the 

 fact without giving any details, which I hope to be able to do 

 later. 



The Excretory Organs of Annelids and 

 Platy helminths. 



Two views have been held respecting the relationship of the 

 nephridia in Annelids to those of the Platyhelminths. Ge- 

 genbaur has held (' Comp. Anat./ Engl, trans., p. 177) that 

 there can be no direct homology between the nephridia in the 

 two groups, because, in the Hirudinea at least, these organs 

 are preceded by several pairs of embryonic excretory tubes. 

 On the other hand, Lang aud others believe that " the excretory 

 system of the Platyhelmiuths is the starting point of that of 

 all higher animals," that in fact the nephridia of Annelids are 

 strictly comparable to those of the unsegmented worms. 



The former view has recently been extended and defended 

 with great ability by Dr. R. S. Bergh, of Copenhagen (4). 

 The latter view is the one which perhaps finds the most 

 general acceptance among comparative anatomists. Bergh 

 uses arguments which tend to prove that the provisional larval 

 excretory organs of Poly go rdius, of Eupomatus, and other 

 Polychaeta, of the Hirudinea, of Echiurus, of certaiu Oligo- 

 chseta (lately discovered by Vejdovsky), and of Mollusca, are 

 homologous with each other and with the excretory system of 

 the Platyhelminths ; the permanent nephridia of these various 

 groups are therefore to be regarded as new formations (in the 

 Annelida), or possibly to be derived from the genital ducts of 



