THE ANATOMY. NEPHRIDIA 41 



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

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

 words : ' Las organes segmentaires sont ici trfes rudimentaires, ce qui concorde avec 

 I'absence d'orifice ext^rieur attribuable k ces organes.' This statement was made 

 of Perichaeta posthuma; and later of Perichaeta robusta he wrote, 'Les organes 

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

 ou diss^min^es sur la membrane p^ritoneale que tapisse la cavity gdndrale'; further 

 on, in the part of his paper devoted to a general resum^ of the anatomy of the group, 

 he speaks of the nephridia forming a 'r&eau glandulaire,' which appeared to him to 

 be an indication of an incomplete suppression of these organs. 



In a communication addressed to the Roj'al 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 Peridiaeta 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 australis ; 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 aU the species have a plectonephric 

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

 Beinodrilus*, Plagiochaeta*, Benhamia*, Trigaster*, Cryptodrilus, Megascolides, 

 JDigaster*, 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. 



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