THE BRITISH FRESH-WATER PLANARIANS. 
17 
Planaria abscissa Ijima. 
Planaria montana Chichkoff. 
Description. Length 16 m.m. ; width 5 m.m. Colour grey, greyish- 
brown, brown, or dark green. Sometimes almost colourless specimens 
are found, which show a reddish or greenish colour in the intestine. Ventral 
surface lighter than dorsal. Tentacles well developed and pointed. Eyes 
small, in the centre of small colourless oval areas close together, and some 
distance behind the base of the tentacles. Mouth three-quarters of body 
length from frontal margin. Genital pore just behind the mouth. Lobe- 
formula of intestine 16-20, 2 (8-10), 16-20. 
Habits. Found in cold springs and mountain streams. 
For an account of distribution and temperature see p. 10. 
The cocoons are spherical and about 1.6 m.m. in diameter, and 
contain from 15 to 30 embryos. They are produced in winter 
as a general rule, but in very cold situations they are deposited 
throughout the year. Transverse fission is common (p. 9). 
Distribution :— 
Britain. Edinburgh Castle (Dalyell 6) ; Bavelaw, nr. Edin¬ 
burgh (water temperature n°C.) (H.W.). Isle of Man. 
Ireland, France, Pyrenees, Belgium, Switzerland, Germany, 
Austria, Sweden. 
Polycelis nigra Ehrenb. Fig. 8. 
Synonyms : Fasciola nigra Muller. 
Planaria nigra Muller. 
Polycelis tenuis Ijima. 
Description. Length may attain 12 m.m. ; width, about 1.5 m.m. 
The numerous eyes, represented by black dots running along the frontal 
margin and about one-third down the lateral margins of the body, together 
with the absence of tentacles, distinguish this species from all others. 
The frontal margin is slightly convex with a slight protrusion in the middle. 
The colour is black or dark brown. Light brown specimens, with dark 
stripes, have been regarded as a distinct species, but are now considered 
to be a variety ; var. brunnea. The mouth is a little less than two-thirds 
the body length from the frontal margin. Intestinal lobe-formula 12-16, 
2 (4-6), 12-16. 
Habits. ' Found in ponds, ditches and streams and can with¬ 
stand a wide range of temperature. The cocoons are deposited 
on the shaded parts of water plants from spring to autumn. 
They are brown, spherical or ellipsoid, and about 1 m.m. in 
diameter. Dalyell observed, in August, 1812, that sexual union 
took place and as he was not aware that planarians are hermaphro¬ 
dite he regarded the smaller specimens as males. Each cocoon 
contains several embryos and incubation takes place in from 21 
B 
