1892.] FROM ALGERIA AND TUNISIA. 35 



pair, although they lie chiefly in segment iii. in front of the nerve- 

 cord, open on to the exterior between segments i. andii. On account 

 of the large terminal end sac, which is prolonged on both sides of 

 the aperture, and may be thus said to have a caecum, it is always 

 easy to make out the external aperture. I am therefore able to be 

 confident about this point, which distinguishes the present species 

 from both Microscolex dubius and Microscolex modestus, and allies 

 it with Microscolex algerieiisis. The external pore is to the inside, 

 and slightly in front, of seta 3 '. 



The three strongly developed hearts of segments x., xi., xii. are 

 present in Microscolex poultoni. 



The generative organs show no great differences from those of 

 other species. As in M. algeriensis, the true vasa deferentia retain their 

 independence until close to the external aperture ; they pass a 

 short way beyond the muscular duct of the atrium, and unite to 

 form one tube, which is surrounded vvith a thick layer of muscular 

 fibres chiefly circular ; this tube is quite indistinguishable in its 

 structural characters from the muscular duct of the atrium ; in a 

 section the two tubes cannot be distinguished except by their 

 position. In the thickness of the body-wall, and near to the 

 external pore, they unite. The penial setae have already been 

 referred to. 



The sperm-sacs are racemose, and occupy the same position as in 

 Microscolex algeriensis and all the other species of the genus. 



The funnels of the sperm-ducts are larger and more folded than in 

 that species. 



I could find neither spermatothecae nor egg-sacs. 



This latter character coimects Microscolex poultoni with lU. dubius, 

 but it is quite clear from the above description that the species 

 described here is perfectly distinct from M. dubius. 



The principal diHerences are : — 



(1) The fusion of vasa deferentia in M. dubius to form one 



tube, which opens into the muscular tube of its prostate. 



(2) The commencement of the nephridia in 'the vth segment in 

 31. dubius. 



(3) The absence of any alteration in the position of the seta 

 on the clitellum in M. dubius. 



It shows much the same resemblances to M. dubius that M. al- 

 geriensis shows to M. modestus. If Dr. Rosa were not so careful a 

 worker as he has proved himself, I should be almost inclined to 

 suspect an identity. 



The genus Microscolex has been investigated by Rosa and 

 Fletcher. It was first met with in Italy by Dr. Rosa ", who, in a later 



^ The ventralmost seta oa each side is seta 1, the nest seta 2, &c. 

 ^ " Microscolex modestus, n. gen., n. sp.," Boll. Mus. Zool. Torino, vol. ii. 

 no. 19 (3 cuts). 



3* 



