THE ANATOMY. NEPHRIDIA 41 



a nephridial system of a different kind. PKHRIER first called attention to the peculiar 

 character of the excretory system of Peiwkaeta, which he described in the following 

 words : ' Les organes segmentaires sont ici tres rudimentaires, ce qui concorde avec 

 1'absence d'orifice exte"rieur attribuable a ccs organes.' This statement was made 

 of Perichaeta posthumu; and later of Perichaeta robutsta he wrote, 'Les organes 

 segmentaires, sous forme de tubes extremement delicate, sont adherents aux cloisons, 

 ou disse'mine'es sur la membrane pe'ritone'ale quo tapisse la cavitd ge'ne'ralu'; further 

 on, in the part of his paper devoted to a general resume* of the anatomy of the group, 

 he speaks of the nephridia forming a 're"seau glandulaire," which appeared to him to 

 be an indication of an incomplete suppression of these organs. 



In a communication addressed to the Royal Society of London (10), I pointed 

 out that in Octochaetus multiporus there were more than a single pair of nephridio- 

 pores to each segment of the body ; and that in the interior of the body the nephridia 

 were divided into eight tufts in each segment, corresponding with as many external 

 pores. In a later paper (47) I corrected the number, having found a much larger 

 number of orifices. The next statement upon the subject was by BENHAM, who found 

 in a species of Perichaeta a large number of small and separate nephridia. He 

 referred in this paper to my own simultaneous discovery of a similar condition in 

 another species of that genus. These results were published later ; I showed that in 

 one species of Perichaeta there were a large number of external excretory pores, perhaps 

 a hundred or so in a segment ; later still the funnels of these were discovered. My 

 results and those of BENHAM were confirmed by SPENCER for a large Cryptodrilid 

 from Australia Megascolides auntralis ; but SPENCER, in addition to the network 

 of small tubes with many external pores, found in the posterior segments of the body 

 a series of larger tubes with funnels not possessed by the smaller tubes. Since these 

 various papers were published a large number of species of earthworms have been 

 described which possess an excretory system of this type, which has been called by 

 myself 'diffuse' and by BENHAM ' plectonephric '. It characterises some or all of the 

 species of the following genera (those in which all the species have a plectonephric 

 excretory system are marked by an asterisk) : Perichaeta*, Megascolex*, Octochaetus*, 

 Deinodrilus*, Plagiochaeta*, Benhamia*, Trigaster*, Cryptodrilus, Megascolides, 

 Digaster*, Microdrilus*, Dichogaster*, Typhoeus*. All these genera, it will be noticed, 

 are members of three families Perichaetidae, Acanthodrilidae, Cryptodrilidae, which 

 I unite here into one super-family Megascolicidae. In no other worms is this ' 

 condition of the nephridial system met with, though I shall point out later, some 

 Eudrilids are provided with an integumental nephridial network which is somewhat 

 analogous. 



