116 PLANARIA. 



In crawling up the side of a vessel, it is liable to drop to the bottom, 

 but its descent seems to be retarded by an invisible thread. Marine. 

 The specimen survived several weeks. 



PLATE XVI. 



FIG. 20. Planarla variegata, enlarged. 



^. PLANARIA ALBA. Plate XVI. Figs. 21, 22. 



Length nearly three lines ; thickness the fifth or sixth of the length ; 

 body roundish ; extremities obtuse ; anterior extremity the smallest. 

 Two. circular very black eyes, at about the fifth of the whole length, be- 

 hind the anterior margin ; colour pure white ; motion smooth and gliding ; 

 intestinal organ not pinnate. Marine. 



PLATE XVI. 



FIG. 21. Planaria alba, enlarged. 



22. Anterior portion, shewing the position of the eyes, enlarged. 



h. PLANARIA GRACILIS Slender Planaria. Plate XVI. fig. 23. 



Length a third of a line ; body rather linear, flattened ; eyes two, 

 black towards the upper surface ; mouth apparently below, under the 

 eyes ; colour white ; motion swift, swimming through the water. Several 

 specimens taken during June in Lochend. 



PLATE XVI. 



FIG. 23. Planaria gracilis, magnified. 



i. PLANARIA EXIGUA. Plate XV. Figs. 13, 14. 



Length a third of a line ; form a double cone when in motion ; two 

 black eyes on the surface of the neck ; colour of some specimens reddish 

 in the middle, and when crawling too near the edge of the water, they 

 contract into a reddish spot and perish ; motion swift. A dark globular 



