134 Transactions. — Zoology. 



lum of P. smithii therefore occupies three segments and a por- 

 tion of a fourth, commencing on the tenth and ending at the 

 posterior border of the thirteenth segment. It forms a complete 

 girdle round these segments — i.e., there is no ventral space not 

 invaded by the glandular modification of the integument. 

 The clitellum therefore includes all the apertures of the gene- 

 rative ducts, which are thus in the strictest sense ' intra- 

 clitellian.' 



" Vascular System. — The vascular system of P. smithii 

 consists, as in the other two species of the genus, of a dorsal 

 and ventral trunk, which are united by transverse branches. 

 The dorsal and ventral vessels are connected in each posterior 

 segment by a transverse pair of trunks, which do not pass 

 straight from the dorsal to the ventral vessel, but have a very 

 sinuous course. The coils of these lateral vessels are not, 

 however, so complicated as in the anterior segments, and their 

 calibre is also less. The vessels, moreover, are not invested 

 by a thick sheath of peritoneal cells like the anterior lateral 

 trunks. The vascular trunks of these posterior segments are 

 precisely like those of Plircoryctes filiformis, as described and 

 figured by Vejdovsky. In P. menkeamis the lateral trunks are 

 only connected with the ventral vessel ; they arise from the 

 latter, and pass round the circumference of the cceloni for a 

 considerable distance, but do not join the dorsal vessel. 



" Reproductive Organs. — The testes are, as stated before, two 

 pairs, situated in segments x. and xi. ; they are not, however, 

 of a simple conical form in the fully-developed worm, but pro- 

 longed into several processes ; the digitate shape is due to the 

 rapid and unequal proliferation of the testicular cells. The 

 genera Lumbricus and Alloloboplwra (among others) have been 

 distinguished by the form of the testes, which have been figured 

 as of conical form in the one, and digitate in the other : it is 

 very possible that this difference does not really exist, but that 

 it is merely due to the stage of development at which the organs 

 have been studied ; such a difference occurs, at any rate, in 

 Plircoryctes. 



" Vasa Deferentia.— Theve are two pairs of these ducts, 

 which open independently of each other on to segments xi. 

 and xii. The first pair do, indeed, open near to the ventral 

 pair of setae between these and the dorsal pair ; but the second 

 pair are a little different. The vas deferens of each side is 

 much shorter, and opens well in front of the ventral pair of 

 setae of the twelfth segment, though behind the groove which 

 separates this segment from the eleventh : that there is really 

 this somewhat unexpected difference between the two pairs of 

 vasa deferentia I have been able to prove by longitudinal sec- 

 tions, which are much better than transverse sections for de- 

 monstrating such a point. In preparation of the worm, 



