122 OLIGOCHAETA 



in various Geoscolicidae are nearly or always so accompanied tty glands. This 

 obviously suggests some relation between the setae and the glands. It looks as 

 if the long setae had the function of either conveying by capillary attraction the 

 secretion of the glands or opening wider an aperture for the passage of the secretion. 

 It seems likely that that is the function of those setae which are developed in the 

 neighbourhood of the male-pores, perhaps more specially those in which the spermi- 

 ducal glands and sperm-ducts open by a common pore ; they would facilitate the 

 passing of the sperm and the secretion of the spermiducal glands. In the Acantho- 

 drilidae, on the other hand, where the spermiducal glands open at some little 

 distance from the sperm-ducts, the function would seem to be rather that of grappling 

 the integument in the neighbourhood of the spermathecal pores in another individual ; 

 here, however, it is possible that the sperm, when liberated from the male-pore may 

 flow along the groove which connects this pore with those of the spermiducal glands, 

 and may at these points mix with the secretion of the spermiducal glands, and be 

 with it conveyed to the spermathecae of the other individual. Genital setae 

 associated with the male-pores only occur in the Megascolicidae, the Eudrilidae, 

 and (rarely) in the Geoscolicidae, Lumbriculides ; in fact, they only occur in those 

 families of terrestrial Oligochaeta in which the male-pores are provided with spermi- 

 ducal glands. They do not, however, often occur in the aquatic families which have 

 also such glands. Though their range of occurrence is thus a wide one, they really 

 are found in comparatively few species ; it is unnecessary here to give a list, which 

 can be compiled from an inspection of the systematic part of this work. Naturally, 

 too, the exact shape of the setae differs ; but in most cases the extremity is beset 

 with spines, a state of affairs, however, which^ is by no means universal ; in many 

 species of Acanthodrilus, for instance, the penial setae are quite smooth throughout. 

 It is an interesting question as to whether these genital setae are new and 

 special structures, or whether they are to be derived from the ordinary setae of the 

 body which have become modified and converted to a new function. The second 

 alternative is evidently the one which is most likely on a priori gi-ound to be true ; 

 and, as a matter of fact, I believe it to be the true view of the origin of the setae. 

 It will be noticed in the first place that when such modified setae are present the 

 ordinary setae are wanting; they are present in the immature worms, but drop out 

 when the genital setae make their appearance; and the genital setae as a rule 

 occupy exactly the place of the missing ordinary setae. There are, too, not wanting 

 transitional forms between the ordinary setae of the body and the modified genital 

 setae ; I have pointed out in Odochaetus antarcticus that the genital setae are much 

 less specialized than in the nearly allied Odochaetus multiporus. On the whole, 



