132 



OLIGOCHAETA 



Fig. 35- 



replaced by long ornamented setae, agreeing very closely in appearance with the 

 penial setae (on the seventeenth and nineteenth segments) of the same worm. These 

 setae are enclosed in a thin, muscular sac, on either side of which is 'a long some- 

 what sausage-shaped glandular body, which communicates by a slender duct with 

 the orifice through which the setae project on to the exterior.' The minute structure 

 of these glands is unfortunately unknown. 



Among the aquatic Oligochaeta the only species 

 with any appendages comparable to the above is 

 Psammoryctes barbatus. In this Tubificid there 

 is a sac (see fig. 35) containing a single penial 

 seta opening either into the spermatheca, just at 

 its external orifice, or independently, but close 

 to it. Two glandular sacs pour their secretion 

 out on to the external surface by the same 

 pore. 



Of the origin of the spermathecae it is difficult 

 to offer any hypothesis that is convincing. BERGH 

 regards them as quite new structures developed 

 for the purpose that they have to perform ; it 

 seems to be not proved that they have any 

 connexion with the nephridia (see above). The 

 occasional close relations in the way of position 

 which the spermathecae have to some of the 

 genital ducts, suggests a possible origin for them 

 as diverticula of such ducts. In the genus Phreo- 

 drilus I have described a long coiled diverticulum 

 of the sperm-duct, which shows, at any rate, that 

 such diverticula can exist ; 1 have suggested that 

 the meaning of this diverticulum may be that 

 it is a rudimentary second sperm-duct. In the 

 Eudrilid Alvania the oviduct has a similar though 

 smaller diverticulum ; if these diverticula became separated from the ducts of which 

 they are outgrowths, and acquired an independent opening on to the exterior, they 

 would be of the same character as the spermathecae. Beyond these scanty facts, 

 however, there is no evidence of such an origin of the spermathecae, probable 

 enough though it is on a priori grounds. In Eudrilus, of course, the spermatheca 

 is a diverticulum of the oviduct, but this instance can hardly be made use of 



SPERMATHECA OF PSAMMORYCTES 

 BARBATUS. 

 (After Stole.) 



A. The entire spermatheca. B. The distal 

 extremity more highly magnified. i. Genital 

 seta. 2. Epithelium at opening of glands (4). 

 5. Formative cells of genital seta. 



