51 
PIT FISH. 
A STRANGE HABITAT FOR GAMMJRUS DUEBENL 
By a. meek, M.Sc. 
Ill the report of last year, I mentioned that Gaynmarits dueheni 
had been sent to me from the Mill Bit at Blyth. This year I put 
myself to some trouble to find out how the creature had got into such 
a pecular situation, and the results of my enquiries I now wish to 
briefly describe. 
Gammarus ducheni is an amphipod crustacean which occurs in 
brackish water near the mouths of rivers, and also in some places 
high up oil the rocks at the sea-side. The genus furnishes two very 
common shore species, and one of these, Gammarus marlnus, may be 
found with young specimens of the shore or dog crab some distance 
up our rivers. But these give place a little higher up to Gammarus 
ducheni or its near ally, Gammarus campijlops, in situations where the 
pretty and interesting Xcomysis vulgaris is also to be procured. 
I have to thank my friend Mr. W. E. Forster, for drawing my 
attention to the new and remarkable if accidental habitat of Gam- 
marus duehenl, a habitat nevertheless to which the creature has 
successfully become adapted, every phase of its life-history being 
passed in it. Mr. Forster informed me that the men who worked in 
the Mill Bit had mentioned to him that “ pit fish ” lived in the water 
in the pit, and when specimens were sent to me, I found them to be 
the crustacean named. They agree in every morphological detail 
with the Gammarus dueheni found in the usual positions, but they 
are ([uite colourless. That is to say, the colour, instead of being as 
it usually is, a uniform brownish-green with three red spots definitely 
placed on the side of the body, is a dull transparent white with no 
red spots. The normal colour is, however, gradually regained when 
the Gammarus is removed from the pit, the time required for the 
process depending upon the degree of exposure to the light. For 
example, a number of specimens were procured on July 8th, and 
three were placed in a glass vessel opposite a window. In about a 
fortnight, on the 21st, one was found to have become slightly yellow 
in colour. It was not until the 20th, however, that a faint lemon 
yellow tinge was seen on the remaining two. On July 30th, two 
(males) were found to have become light brown in colour, and the 
three red spots were now to be seen also. The latter however, were 
light red to begin with, but in a short time gained in intensity with 
the general colour of the body. The three subsequently became like 
