ON H^EMONAIS LAUREN TIL 111 



elongated antero-posteriorly ; sections show it to be markedly bifid in front and 

 behind. 



Asexual reproduction was taking place in a number of specimens ; chains of 

 more than two were not observed, and are probably not formed, since the posterior 

 animal appears to separate at an early stage, some time before the complete develop- 

 ment of the anterior ventral setae and complete differentiation of the head end ; 

 n (the number of segments after which the budding zone forms) = 31, 33, or 36. Four 

 seta-bearing segments, or five and a prostomium in all, are intercalated behind the 

 actual line of separation to form the anterior end of the hinder animal. 



Genital Organs. — All the specimens first obtained, and used in writing the fore- 

 going account, were without sexual organs ; but by a lucky chance an examination of 

 other material from the same pond at a later date (May) showed a few specimens 

 with well-developed sexual apparatus, as well as one or two in an earlier stage. In 

 order to avoid possible injury or accidents, the specimens were examined only 

 cursorily while alive ; and having been fixed almost at once, were subsequently 

 investigated by means of longitudinal and transverse sections. 



The gonads appear before the rest of the reproductive apparatus, and disappear 

 entirely before this has reached its full development. In the specimen in which they 

 were seen no other portion of the genital system was present. The testes (fig. l) 

 consisted of paired masses of cells, of considerable size, in segment v, springing by a 

 narrow "base from the posterior face of septum 4/5 close to its attachment to the 

 ventral body-wall. The ovaries, smaller in this specimen than the testes, were 

 similarly situated in the next posterior segment. 



In fully developed specimens the clitellum extends over the posterior half of 

 segment v, segments vi and vii, and_a small part of viii — nearly three segments 

 altogether. The epithelium (figs. 4, 5, 6) consists of much-elongated cells which 

 show a coarsely reticular structure, the meshes of the network constituting the 

 boundaries of clear spaces with non-staining contents ; the nuclei are in two layers, 

 one on the surface, the other at the base of the cells. The clitellum is absent from 

 a transverse strip between the male apertures (fig. 5). 



The sperm-sac, a backward out-pushing of septum 5/6, extended as far as 

 segment ix in a specimen which was not fully mature. In a later stage, when the 

 accumulation of ova behind it has increased, and, when, perhaps, its contents have 

 been partially discharged, it may be practically confined to segment vi. 



The male funnels lie in the anterior part of the sperm-sac. They are cup- 

 shaped, with everted ciliated margin ; the mouths look upwards and backwards. 

 The funnels touch each other -at their inner borders in the middle line, dorsal to the 

 alimentary canal. The wall of the sperm-sac fuses with the outer surfaces of the 

 funnels (fig. 4). 



The vas deferens is short and stout, with a slightly twisted course and a consider- 

 able lumen ; it descends to enter the atrium towards its upper surface. Its diameter is 



TRANS. ROY. SOU. ED1N., VOL. L, PART IV (NO. 20). 107 



