ON MONOPYLEPHOEÜS LIMOSUS. 43 



chamber unprovided with any chitinous lining ; this in its turn 

 communicates with the exterior by a comparatively small pore in 

 segment 11. It is to the wall of this chamber that the fibres above 



mentioned are attached The duct opens on a slight papilla 



into a small penial chamber, an invagination of the epidermis." 

 " There are sperm-sacs in 9, and an unpaired one passing through 

 segments 11 to 19." The above quotations are all from Benham. 



On the formation of spermatophores in this species Benham 

 says that, " The ampulla is filled with spermatozoa, without any 

 arrangement or order ; but in the globular sac the sperms are 

 orientated, so that the heads are towards the epithelial cells, and 

 it appears that each cell has many sperms associated with its end. 

 Hence I conclude that spermatophores are formed." But the word 

 ' spermatophore ' of aquatic oligochaetes is not generally used in 

 such a sense and in my opinion it seems to be better to conclude 

 that spermatophores are not formed. 



Benham does not give any description of the main vascular 

 system of this species, and consequently I can not decide whether 

 it is to be referred to the genus Monopylephorus Levinsen or Rhiso- 

 drilus Smith, but from his statement that, " there is an elaborate 

 integumental blood-plexus," it appears to me very probable that it 

 belongs to the former genus. 



As may be seen from the foregoing, Monopylephorus limosus 

 diners from the above mentioned species by its setae and the 

 structure of its nephridia, alimentary and genital systems. The 

 following characters are common to all of them, and may be looked 

 upon as generic ones : 



1. The absence of setae on the ventral side of segment XI. 



2. The presence of numerous cœlomic corpuscles. 



3. Nephridia : 



a. The main mass closely adheres to the ventral vessel. 



