144 Proceedings of the Royal Irish Academy. 



The genus Stylodriliis has hitherto been distinguished from all other 

 European genera of the Lumbriculidfe by the absence of these blind 

 appendages. The genus was founded by Claparede in 1861. Speaking of 

 S. heringianus, the first known species, he says (5. p. 264) : — " The vascular 

 system is formed of dorsal and ventral vessels placed in communication with 

 each other, in each segment, by an intestinal branch and a perivisceral branch." 



The second species, S. gabretce, was described by Vejdovsky. With 

 reference to the vascular system, he says (28. p. 53) : — "The blood-vessels do 

 not show lateral branching." The remaining species, >S'. Vejdovskyi, was 

 described by Benham, who makes only a slight reference to the vascular 

 system, from which one may infer that it is not remarkable in any way. 



The present species differs markedly in its vascular system from all other 

 members of the genus. The commissural vessels, instead of being two pairs 

 in each segment, as Claparede says, are confined to the anterior 13 segments. 

 There are two pairs of them in each of the segments ; and they are very 

 long and folded. The vessels of the 13th segment are extremely long in the 

 mature animal, and ramify freely over the walls of the ovisacs and sperm- 

 sacs, increasing in length as these develop. They often extend back so far 

 as the 21st segment. Behind the 21st segment there is no direct connexion 

 between the dorsal and ventral trunks. 



The ventral vessel is formed in the 5th segment by the union of the two 

 anterior commissures. As the dorsal vessel is traced backwards, it begins to 

 show indications of short, blind offshoots. In the last 30 segments or so of 

 the tail these become very conspicuous. There are two pairs in each segment, 

 situated close to the anterior and posterior septa respectively (fig. 8, G, a). 

 They are clearly homologous to the more highly organized blood-glands of 

 the other Lumbriculid genera. They are peculiar in being extremely thin- 

 walled and free from the covering of chloragogen cells. They project freely 

 into the body-cavity when full of blood, and are almost invisible when empty. 

 The dorsal vessel expands before the blind sacs. In tracing the ventral 

 vessel backwards from the 13th segment, it is seen to give off occasionally a 

 median dorsal branch, which enters the wall of the intestine. In the tail 

 these vessels become much more numerous, 4-6 of them occurring in each 

 segment. Just before entering the wall of the intestine, each vessel divides 

 into two branches (figs. 8, c, e ; and 8, G, b). The ventral vessel is slightly 

 contractile behind. 



Three transverse sections through one of the posterior segments are 

 shown in iig. 8, f. In No. 1 the section passes through the dorsal vessel and 

 one of the blind sacs. In No. 2 it cuts both the blind sacs. This section 

 also shows one of the branches passing from the ventral vessel into the wall 



