1887-] ANATOMY OF KARTHWORMS. 391 



body by being longer and thinner. In Urocheeta one or more pairs 

 of the cUtellar setae are larger and beset with a number of transverse 

 notches. I hare recently described an identical modification in the 

 clitellar setae of the closely allied genus Thamnodrilus ^ Horst dis- 

 tinguishes ^ the clitellar tetse of Rhinodrilus by their greater size. 

 In Lumbricus the modification of the setae is not confined to the 

 clitellum, but is also found in the neighbourhood of the generative 

 orifices. 



I believe that in the genus Perichceta no modification of the setae at 

 all comparable has ever been described except by myself in P. armata 

 and P. ceylonica. The first-named species is remarkable for the fact 

 that the terminal part of the ejaculatory duct opens on to the exte- 

 rior in common with a thin-walled muscular sac, the interior of which 

 is filled with a number of peculiar setae, the shape of which can be 

 best appreciated by an inspection of the figure which accompanies 

 my memoir. Perichceta ceylonica is the only other species of the 

 genus in which this arrangement is repeated, and the arrangement is 

 practically ideutical with that which obtains in P. armata. It is 

 perfectly clear that these sacs of penial setae correspond in every 

 way to the penial setae occasionally developed in other Earthworms 

 lor example in the genera Acant hodrilus and Typhoeus. In Acantho- 

 drilus it is certain that peiual setae are not supernumerary structures 

 developed only at the period of sexual maturity, but they replace the 

 ordinary setae of the pair which correspond to the male geneiative 

 aperture. 



EXPLANATION OF PLATE XXXIII. 



Fig. 1. Transverse section of vas deferens ; higlily magnified. 



2. Testis (J) and vesicula seminalis {v.s). 



3. TransTerse section of oesophagus and ventral gland of 11th segment. 



d, dorsal blood-vessel ; si, supra-intestinal (double) ; h, heart ; h' , 

 branch sujaplying walls of oesophagus and gland ; ]p, peritoneal coat. 



4. Section through gland (rudimentary ovary?) attached to wall of 13th 



segment. 6, gland ; a, muscular tube enclosing it ; to the left the 

 tube is seen to form a bend and to be cut across twice. 



5. Ventral aspect of oesophagus in segments 10 and 11, to show suboesopha- 



geal glands (a). Bifurcation of subintestinal vessel illustrated in this 

 figure. 



6. Lateral view of same region. Bifurcation of supraintestinal vessel, as 



well as subintestinal vessel, illustrated. 



7. Transverse section of oesophagus in 10th segment ; left-hand figure 



through opening of suboesophagcal gland (highly magnified in fig. 3), 

 right-hand figure in front of or behind opening of gland. Compare 

 with figs. 5 and 6. 



8. 9, 10. Transverse sections through prostate gland at various levels. 



11. Opening of vas deferens funnel into vesicula seminalis. a, vesicula 



crammed with developing spermatozoa ; c, ciliated funnel ; b, vesicle 

 of vas deferens. 



12. Section of oviduct, to show eiUated epithelium and muscular waUs. 



13. A portion of fig. 8 more highly magnified. I, lining epithelium; e', 



glandular cells ; m, transverse longitudinal muscles. 



14. Section of epidermis, a, problematical body ; b, glandular cells. 



' P. Z. S. 1887, pt. i. * Notes from Leyden Museum, 1886. 



