57 
leDgth; the sLort oesophagus is about the same length as the 
pharynx, the intestinal lobes being rather thick and entering the 
abdomen more or less, according to the state of contraction. The 
excretory system consists of a single ventral stem, dividing in front 
of the ovary into two branches which join dorsally in front of the 
pharynx. The testes are placed one in front of the other, behind 
or to the right side of the vesicula seminalis, and behind but close 
to the ventral sucker. Anterior testis (0-08 mm.) smaller than 
the posterior (0-10 mm.), each giving off a short vas deferens which 
joins the vesicula seminalis without uniting with its fellow. The 
vesicula seminalis is placed directly behind the ventral sucker, and 
divided into two portions, both thin-wallcd and spherical, the 
hinder part slightly the larger. The anterior part is separated 
from the pars prostatica by a constriction. The pars prostatica 
is long and winding, with large gland cells ; at about the level of 
the fork of the intestine it is joined by the uterus, and a cylindrical 
cirrus sac (026 mm. long) surrounds the common duct. This is 
striated for the first three-quarters of its length, and then covered 
with small papilhe. It opens ventrally by the side of the pharynx, 
or in front of it. The ovary is circular, and placed slightly behind 
the last third of the soma ; posteriorly the oviduct gives off a 
globular receptaculum seminis. The uterus is winding, with many 
loops, and enters the abdomen in extended specimens, and the 
loops wind almost all over the body until they reach the ventral 
sucker, where the oviduct runs forward to join the male duct. 
The eggs arc a clear greenish-yellow, very numerous, and measuring 
0-2G mm. by 0-01 mm. The two vitellaria are globular, or more 
or less ovate, and arc about the same size as the ovary, and imme- 
diately behind it. Each gives off a duct which unite and open into 
the oviduct near the receptaculum seminis. 
The life history is not known. Odhncr, however, suggests that 
Pratt's North American Hnniuius appmcHcutahts, the life history 
of which he has traced in a species of copepod,* is likely to be 
this species, although the presence of a simple and not bilobed 
vesicula seminalis, as Odhner says, is against this. At any rate, it is 
some closely allied form, and indicates the direction in which to 
look for the life histories of other Hemiurids. In this paper Pratt 
gives a most interesting account of this larval Trematode which 
he proves to inhabit the copepod from its earliest larval stage up 
to its encysted condition, no intermediate host being involved. 
