208 W. B. BENHAM. 



The excretory system has quite recently had a new light 

 thrown upon it by the researches of Beddard^ and of Baldwin 

 Spencer." 



Perrier, in 1872^ noticed that the nephridia were replaced in 

 Perichseta by small tufts of tubules ; and a similar arrange- 

 ment is found in many other worms. 



Beddard^ described a species of Acanthodrilus with eight 

 "nephridia" per somite; these he more recently* discovered 

 were not really large tubules, but eight groups of small tubules 

 opening to the exterior by numerous apertures. Again, more 

 recently he has shown us that in Perichseta armata there is 

 a network of delicate tubules in addition to a pair of large 

 nephridia in each somite ; and this network of delicate tubules 

 is provided with many external apertures, sometimes without 

 internal funnels, rarely with them. 



Baldwin Spencer, in his detailed description of Megasco- 

 lides australis, demonstrates the transition between the 

 large nephridia in the posterior part of the body and the deli- 

 cate small tubules which line the inner surface of the body- 

 wall in the anterior somites. Anteriorly there is a network 

 of these delicate tubules, which have no internal funnels, but 

 numerous external openings, the network being continuous 

 somite to somite. About the middle of the body this net- 

 work becomes confined to a band of small tubules round the 

 somite, of which one tubule is larger than the rest. Further 

 back this tubule increases in size, and ultimately attains a size 

 almost equal to that of a nephridium in Lumbricus; more- 

 over, this tube communicates with the coelom by means of a 

 funnel, but still retains a connection with the network of 

 smaller tubules. Both Beddard and Spencer favour the idea 

 of the development of a " nephridium'^ from such a network 

 of tubules. 



1 Beddard, ' Quart. Journ. Micr, Sci.,' vol. xxix, and see literature therein. 



2 Baldwin Spencer, "The Anatomy of Mega scolides australis," 'Trans. 

 Eoy. See:, Victoria,' vol. i, 1SS8. 



3 Beddard, ' Proc. Boy. Soc.,' 1885. 



•» Beddard, ' Quart. Journ. Micr. Sci.,' vol. xxviii. 



