324 OLIGOCHAETA 



is also marked externally by a slight swelling l ; MICHAELSEN thinks that these 

 tracts of cells serve as sense-organs related to the generative function ; the swellings 

 are thus distributed in the three species in which they occur : in P. maximus in 

 xiv, xv, xvi ; in P. lineatus in xiii, xiv ; in P. nervosus in xiii, xiv, xv (according to 

 EISEN in iv, v, xii as well). 



Since the investigations of MICHAELSEN, UDE (1) has recorded the discovery of 

 the ventral organs in P. pagenstecheri ; but no details are given, except that it is 

 said that the organs most resemble those of P. lineatus. I am disposed to agree 

 however with HESSE and to look upon these organs as copulatory glands. 



MICHAELSEN allows eleven species to the genus. They are these : 



(1) Pachydrilus lineatus, O. F. MULLER. 



(2) Pachydrilus nervosus, EISEN. 



(3) Pachydrilus profugus, EISEN. 



(4) Pachydrilus verrucosus, CLAPAREDE. 



(5) Pachydrilus pagenstecheri, RATZEL. 



(6) Pachydrilus krohnii, CLAPAKEDE. 



(7) Pachydrilus subterraneus, VEJDOVSKY. 



(8) Pachydrilus catanensis, DRAGO. 



(9) Pachydrilus maximus, MICHAELSEN. 

 (10) Pachydrilus minutus, O. F. MOLLER. 

 (n) Pachydrilus fossarum, TAUBER. 



Of these eleven, MICHAELSEN separates P. krohnii and P. catanensis as ' species inquirendae.' 

 He also remarks, with reference to P. fossarum, that in the absence of further details than are 

 given in TAUBER'S and LEVINSEN'S descriptions of this species, it cannot be regarded as certainly 

 a ' good ' species. VEJDOVSKY, however, accepts it, but without giving any reasons for so doing. 

 Tauber's definition is this : ' Corpus, 20-40 mm. longum, postice attenuatum, ex segmentis 40-80 

 constans. Setae minutae, apice leviter curvatae, 4-9 in quoque fascicule. Sanguis respiratorius 

 purpureus. Color antice albidus, postice fuscus. Vitellus ruber. Ova niense Aprili-Junio in capsulis e 

 stiutis superioribus deciduisque clitelli formatis, multa in quaque capsula deponuntur. Variat rarior 

 albidus.' 



LEVINSEN (2, p. 231) adds to this definition that the worm has a spermatheca with a duct distinct 

 from the main pouch, and that the duct of the nephridia comes off from the middle of the organ, and 

 not, as is usually the case, from the extremity. That the species is really a Pachydrilus is evident from 

 the facts given by TAUBER ; but there is not, in my opinion, any security that LEVINSEN'S P. fossarum 

 is the same species as that so named by TAUBER. If there were, the species might be regarded as 

 distinct on account of its large size and the origin of the nephridial duct; I prefer to leave the matter 

 as I find it. It should be mentioned that LEVINSEN considers that TAUBER'S P. verrucosus is identical 

 with his P. fossanim, and that, according to MICHAELSEN, P. crassus also (of TAUBER) is the same 

 species. 



1 Cf. Fridericia norae-zelandiae, and Parcnchytraeus. 



