47° 



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, Anoplodium is found upon 

 sea-cucumbers, and Graffilla upon marine gastropods. 



TREMATODES. 



1, Prostomum — «, proboscis ; b, mouth. 2, Convoluta. 

 (Natural size represented by lines. ) 



3, Vortex. 



Schizostoma productum (enlarged 200 times). 



Differing in many important points from the typical Rhabdocoela 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. 



