DESCRIPTIONS OF GENERA AND SPECIES 393 



When present and everted it may be itself sufficient to hold the worms together during 

 coitus. Another character may ultimately prove to be also related ; in no case has 

 the clitellum any setae when the spermiducal gland opens on to the exterior by means 

 of the sac referred to ; here again the converse is not absolutely true. Unfortunately 

 our knowledge of the various species of Perichaeta is not, as yet, sufficiently advanced 

 to permit of a definite statement upon these matters. 



Though the character is an important one, it is one that must be used with 

 caution ; it so frequently happens that a given species varies in the number of the 

 genital papillae, that to state the typical numbers renders necessary the examination 

 of a large number of specimens which is by no means always possible. 



(6) The spermiducal pores and the spermathecal pores are sometimes nearer to and 

 sometimes further away from the middle line. 



(7) The position of the first dorsal pore is another character which must be used 

 cautiously ; the one advantage .which poorly preserved worms have over those which 

 are well preserved is that the dorsal pores are often more obvious. 



(H) In all Perickaetae, with the sole exception of P. ijimae, the spermathecae are 

 provided with diverticula ; even P. ijimae may prove to be no exception when it is 

 examined microscopically ; for in Octochaetus multiporus the diverticula of the sperma- 

 thecae are not always apparent until the integument in the neighbourhood of the 

 orifices of the spermathecae is examined by means of sections. The number of pairs 

 of spermathecae offer (in conjunction with other points) very good specific characters ; 

 it appears to be only rarely that there is any variation in individuals. In three 

 species, however, such a variation has been recorded ; these are P. ringeana, P. barba- 

 densis, and P. capensis ; in all of these the number varies from two to three pairs. 

 One species only seems to have no spermathecae at all ; this is P. acystis. In two 

 individuals of P. acystis I found a complete absence of spermathecae. The only other 

 very exceptional condition of the spermatheca occurs in P. stelleri and a few allied 

 forms ; here there are a large number of small spermathecae, with diverticula, in two 

 segments. The arrangement of the spermathecae in these remarkable species is only 

 paralleled in the Geoscolicidae. The spermathecae vary but slightly in form ; and 

 with one doubtful exception each spermatheca has but one diverticulum ; this exception 

 is HICHAELSEN'S species P.ferdinandi. In others there appear sometimes to be two 

 or even three diverticula ; thus PERKIER mentioned the existence in P. houlleti of 

 additional diverticula. I showed, however, that these supposed diverticula are really 

 glandular appendices exactly similar to those which are often associated with the 

 genital papillae, and have therefore only an accidental relation to the spermathecae ; 

 ' diverticula ' of this kind are found in P. ^^dekemi, also, a near ally of P. houlleti. 



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