598 WHAITMAN. [Vou. II. 
lateral hearts and the dorsal sides of the testes. Its position is 
thus a little behind the nephridial pore, which opens on the ventral 
surface a little below the lateral heart, in the anterior half of 
the first ring. 
28. There are four longitudinal vessels and as many sinuses, 
one dorsal, one ventral, and two lateral. The dorsal vessel is 
inclosed for the greater part of its length in the dorsal sinus ; 
the ventral vessel lies mostly outside the ventral sinus ; the lat- 
eral vessels lie just above the lateral sinuses, and run parallel 
with them. In the post-clitellar region, a pair of branchial ves- 
sels are given off in each somite from the lateral vessels. Each 
branchial vessel divides into two branches, after passing through 
the muscular strata of the body, one of which passes forward to 
meet a posterior branch coming from the preceding branchial 
vessel, while the other passes backward to meet an anterior 
branch coming from the succeeding branchial vessel. The two 
branches do not actually meet, but rather each enters separately 
the base of the auricular chamber of the heart, where the two 
inflowing currents mingle and ascend to pass through a wide 
common opening into the main chamber. This opening is on 
the dorso-lateral face of the chamber, while the efferent opening 
lies on the ventro-median surface, and leads into the branchial 
sinus, which opens in turn into the lateral sinus, opposite the 
junction of the latter with the segmental sinus. The four sinal 
ostia thus brought together are guarded by peculiar pluriramous 
muscles. The dorso-ventral sinus communicates with the tes- 
ticular sinus, and passes into the segmental sinus just before 
the latter unites with the lateral sinus. The connections be- 
tween the vessels and sinuses at the ends of the body have not 
yet been completely traced. 
29. All the Hzrudinea may be derived from a form in which 
the somite consists of three rings. The 5-ring type of Mephelis 
and Hzrudo has been derived, not from a 6-ring or 12-ring type, 
but from a 3-ring type, by the acquisition of two new rings. 
The position of the nephridial pores in the posterior edge of the 
last ring of the somite, can be accounted for more readily as 
the result of shifting than of a loss of rings. How three rings 
can become 4, 5, 6, or 12, I can promise to make clear in an 
early paper. 
30. Copulation in Clepsine is never direct, z.¢, by union of 
