45 
in apparently complete specimens is somewhat less than 300. The pro- 
stomium is without terminal pore and in some specimens transverse 
grooves are evident. Its length anterior to the mouth is nearly twice its 
width and equals the distance from the mouth to the middle or end of 
the fourth somite. The first five somites are shorter and broader than 
those next following and give the impression of a slight degree of cephal- 
ization, which is also manifest in the internal structure (PI. II, Fig. 7). 
A distinct groove which seems, on the dorsal and lateral walls, to define 
clearly the anterior border of the first somite makes that somite appear 
slightly longer than the second, and apparently locates the mouth-opening 
on the mid-ventral surface of the somite rather than at its anterior 
margin. This leaves but a short interval between the mouth and the 
intersegmental groove 1/2. If a similar state of things exists in other 
species it may account for the apparent extreme shortness of the first 
somite which has often been mentioned. I find a similar condition in 
H. emissarius. 
The ventral setae (Pl. II, Fig. 6) are of the ordinary haplotaxid 
type, with nearly straight inner shaft, slightly developed nodule at about 
one-third of the length of the seta from the distal end, and distal part 
strongly curved. Ordinary measurements are 0.30—0.32 0.022 mm. 
The dorsal setae are very much smaller (0.125 0.007 mm.), begin quite 
uniformly on the fifth somite, and are present on only the next following 
12-20 somites. This character is presumably not of much systematic 
importance but is fairly uniform in a considerable number of specimens. 
The setal distances are approximately indicated by the following formula 
in which / represents the lateral line: aa: al : ld :dd =4:4:3:8. No 
clitellum nor genital papillae have been found. 
INTERNAL CHARACTERS 
The buccal region (Benham, ’04 : 301) is thin-walled and connected 
to the body wall by numerous muscular strands, and extends through the 
first three somites. The gizzard has its chief development in the pos- 
terior part of the fourth, and the anterior part of the fifth, somite, where 
the muscular wall is strongly thickened. The vascular system much 
resembles that already described for other species. The dorsal vessel 
forks just posterior to the brain. The branches extend anteriorly and 
then posteriorly and, after a somewhat tortuous course, unite in the pos- 
terior part of the third somite and form the anterior part of the ventral 
vessel. One pair of slender commissural vessels in each of the setigerous 
somites connects the dorsal and ventral vessels. The connections pos- 
terior to somite 4 are in the posterior part of the somites, close to the 
septa. The connections of the vessels of each of somites 2-4 are in the 
anterior part of the following somite. 
The distribution of the nephridia differs from that usually found in 
the genus, the peculiarities of arrangement being correlated with those 
of the reproductive organs, to be described later. Ordinary nephridia 
like those described in other species of the genus are found in 12-14 and 
