2) 
a) 
NATURAL HISTORY. 
CHAPTER XIII. 
A SMALL FRESH-WATER SHRIMP. 
Gammarus grossi.—Leach. 
This creature belongs to the family Gamma- 
ride of Dr. Leach. In some respects it accords 
with the genus ¢alitrus, the first three joints of 
the superior antenne being shorter than the 
inferior ones, while it agrees with the genus 
gammarus in having bundles of spines at the 
joints above the tail. 
They are often very abundant in ponds and 
rivulets during the spring, and in fine weather 
congregate among confervee and water-plants. 
If kept a few days in a vessel of clean water, 
they become more transparent, and assume a 
more interesting appearance under the micro- 
scope. The body is curved and compressed 
laterally ; it consists of ten segments of a varie- 
gated cinerous colour, with fine touches of 
bright red. The dark alimentary canal is finely 
