Haswett—A Monograph of the Temnocephalee. 137 
of the large crayfish (Astacopsis Franklinit) that frequents the northern rivers of 
Tasmania. 
My specimens of 7. guadricornis have not been very well preserved for minute 
investigation ; but they show some marked peculiarities in the histology when 
compared with the other species. One remarkable feature is the large size of the nuclei, 
and their possession of closely coiled chromatin threads, unlike the nuclei of the other 
species. The cuticle is relatively thin; the epidermis very thick, especially on the 
dorsal surface, and with a very coarsely fibrillated appearance. In sections of parts 
where the rhabdites are passing out, nearly all these fibrillee prove to represent pore- 
canals, which are here very numerous, and, apparently, are quite devoid of the spaces 
found in the other species. The pigment is in larger and smaller rounded granules 
between and beneath the muscular layers. 
6. TemNocePHALA JHERINGH. Plate x. fig. 19, and Plate xv. fig. 2. 
In general shape this species is similar to 7. fasciata and 7. minor. The body 
is dorsi-ventrally compressed, convex above, flat or slightly concave below, of an oval 
outline when looked at from the dorsal or the ventral side. In front are five subequal, 
dorsi-ventrally compressed tentacles. On the ventral surface behind is a sucker of 
circular outline, the margin of which projects backwards a little beyond the posterior 
border of the body, elevated on a short stalk. The mouth is a short, transversely 
directed slit situated on the ventral surface some distance behind the bases of the 
tentacles. The common genital aperture, in the form of a much smaller slit, also 
transverse, is situated some distance in front of the anterior border of the sucker. 
The integument is entirely devoid of pigment, and there are no eyes. 
The pharynx is globular in shape, a little less than the breadth of the body. 
The intestine is squarish in outline ; its walls are folded, but the deep incisions by 
which in the Australian species it is divided laterally are not present, the muscular 
septa being absent. 
The testes are oval, situated close together, altogether behind the intestine, the 
more anterior, which is also more external, having its centre nearly opposite the 
common genital opening. The two vasa deferentia open into the dilated base of the 
cirrus, which forms a vesicula seminalis. The cirrus is nearly transverse in position, 
the free extremity reaching to the middle line. It is funnel-shaped, the wide end 
being continuous with the wall of the vesicula seminalis. At the free end is a 
slight enlargement, probably containing spines. 
The vitelline glands have no tendency to an arrangement in transverse zones, 
such as is discernible in some of the other species. They form an irregular network 
T 
