PLATE IV. 



Fig. 



1. Tetrastemma flavida, Ehrenberg. 



2. Lineus gesserensis, 0. E. Miiller, green variety, showing the generative apertures as a series 



of pale specks along the sides. 



3. Small mucus-cord of the same species, with dull yellowish ova. Enlarged under a lens. 



4. Pale variety of Cephalothrix linearis, Jens Rathke. 



5. Anterior fragment of the same species, with reddish pigment at tip of snout. The digestive 



cavity is tinted of a fine deep green behind the oesophageal region, and the entire surface 

 speckled with minute white grains. 



