1 41] OLIGOCH^TOLOGICAL RESEARCHES. 919 



the penis sheath, and in the latter species this part has, as I think in- 

 correctly, been considered as the atrium proper. In 8pirosperma the 

 lower end of the penis is composed of very large octagonal or rounded 

 cells, quite different in form and size from those which constitute the 

 upper part of the penis and lower part of the atrium, but more resem- 

 bling those of the upper part of this organ. 



Penis is surrounded by a sheath of chitinous consistency in all the 

 genera of the family, except in Ilyodrilus. In Ilyodrilus Perrierii, how- 

 ever, we meet with a chitinous sheath, but it is difficult to decide upon 

 whether this sheath should be referred to the oviduct or to the penis. 



The penis sheath is nearly always free at both its ends, and never 

 attached to the body wall. The shape and relative size of the sheath 

 is always of the utmost importance as characterizing the species ; but 

 as I have in a former part of this paper more minutely described the 

 same, it will now suffice to point out the few principal forms under 

 which all other may be arranged. 



The upper end of the penis sheath is always free ; the lower end is 

 free in TuUficini, but is in Telmatodrilini connected with the apex of the 

 penis proper. That this latter is a more primitive form of the penis is 

 evident, as in undeveloped specimens of TuUficini the penis sheath is 

 always connected with the penis itself, and separates from the latter 

 first in a later stage of development. But to this I will return further 

 on. In Tehnatodrilus the penis sheath is funnel-shaped, the interior 

 end being the widest. In TuUficini the form of the' sheath is either 

 that of a funnel, as in EemituUfex and Ilyodrilus Perrierii, or tube, 

 cylindrical, or trumpet shaped, as in the most of. the species of Limno- 

 drilus and Camptodrilus. In Limnodrilm Silvani we meet with an 

 aberrant form, its penis sheath taking the shape of an arrow-head, at 

 least when seen from the front. The upper end of the penis sheath is in 

 Limnodrilus ornatus furnished with a ring of star-like glands, the func- 

 tions of which are not understood. Generally the penis sheath covers 

 the penis clear to apex, but in Sjnrosperma and Limnodrilus Steigerwaldii 

 the penis protrudes considerably beyond the sheath. 



In adult specimens of Ttlmatodrilus the penis appears to be constantly 

 projecting through the genital poras, but in TuUficini this projection 

 takes place only during copulation. This sexual porus is always found 

 in the tenth setigerous segment, and in TuUficini just in front of the 

 ventral spines, but in Telmatodrilini between the spine fascicle and the 

 ventral ganglion. 



' DEYELOPMENT OF THE COPULATIVE ORGANS. 



Vejdovsky, in his most beautiful work. Monographic der TJnchywtriden* 

 gives evidence of the development of the efferent duct and copulative 

 organ in that family. It is only natural to suppose that the course of 

 development of such an important organ as the efferent duct should be 



""^^^""^^"^^ "~" » Plate I, Fig. 12. 



