470 
WORMS. 
Upon the narrow and pointed head are the two little black eye-spots. In the 
genus Prostomum the mouth (b) is situated in the middle of the ventral surface, 
as in the last, but the slender 
and pointed head - end is 
provided with a distinct 
proboscis (a), which calls 
to mind that of the 
nemertines, inasmuch as it 
is not directly connected 
with the mouth, and is 
contained in a special sheath. 
The posterior end of the 
body, on the contrary, is 
thick, club - shaped, and 
armed with a sharp goad, 
which seems to be used as 
an organ of defence. The 
same illustration shows a 
species of the allied genus Vortex, in which the aperture of the mouth is on the 
under side, near the front end of the body. This mouth leads into a large oval 
gullet, communicating with the long sac-like intestine. The black spot in front 
of the mouth is the eye. In Schizostoma, on the contrary, the mouth which is 
long and slit-like, is situated in front of the two eyes. Some of the allied genera 
lead a parasitic and not a free life. For instance, Anoploclium is found upon 
sea-cucumbers, and Graffi.Ua upon marine gastropods. 
TREMATODES. 
1, Prostomum — a, proboscis ; b, mouth. 2, Convolutei. 
(Natural size represented by lines.) 
3, Vortex. 
Schizostoma productum (enlarged 200 times). 
Differing in many important points from the typical Rhatplocoela is the 
small marine Convoluta, shown in Fig. 2 of the illustration, in which the 
alimentary canal, the excretory organs, and the nervous system have dis¬ 
appeared. Imbedded in the solid tissues of some of the species of Convoluta 
are large numbers of cells containing chlorophyll, or the green colouring 
matter of plants. These cells are probably minute plants (Algce), which have 
taken up their abode parasitically in the worm. In addition to the ordinary 
means of reproduction by sexual organs, some of the rhabdocoelans multiply by 
division. 
