NEW ENGLISH GENUS OE AQUATIC OLIGOCHiETA. 167 



There arenormally three pairs of sperm a the cse in Somites 

 VII, VIII, and ix. Each sac is pyriform, Avith a long duct 

 opening at the anterior margin of its somite in a line with the 

 lateral chsetse. But the number appears to be subject to 

 variation, as I have notes of three abnormalities amongst the 

 score or so of the worm examined, viz. : 



A. Eight side : spermatliecse iu vii, viii ; left side, viii, ix. 



B. „ „ VIII, IX ; „ viii, IX, X. 



C. „ „ VIII, IX ; „ none. 



But in this last case the worm had apparently passed its 

 maturity, as other organs were very small, e. g. sperm-sacs, 

 and it is quite diflficult to see the spermathecse in immature 

 worms ; they were, for instance, overlooked by Beddard in 

 Allurus, probably for this reason. 



§ The Vascular System (figs. 6 — 10). 



It is in the vascular system that Sparganophilus differs 

 most remarkably from other forms. 



The dorsal vessel, which lies freely above the gut, is broad, 

 constricted at the septa, and runs, as usual, throughout the 

 body. In each of the Somites xi, x, and ix it is specially 

 dilated, and frequently slightly curved (fig. 6). In front of 

 Somite ix the vessel suddenly diminishes in diameter to about 

 a third its previous size, and thence runs with a gradually 

 decreasing diameter to the first somite. 



The ventral vessel presents no noticeable feature. Supra- 

 intestinal and subneural vessels are absent. 



In each of the Somites Ji to xi a pair of commissural vessels 

 pass from the dorsal to the ventral vessel. Those of Somites 

 II to VI are small equidiametered vessels, whilst those in 

 Somites vii to xi are much larger, moniliform, and slightly 

 contorted; these are the "lateral hearts" (figs, 6, 9). 



In each of the succeeding somites, with the exception of 

 Somites xii and xiii, a pair of dorsal tegumentary or 

 " peripheral'' vessels is given off by the dorsal vessel, near the 

 hinder septum, which it perforates in order to pass to the 



