142 HISTORY OF BRITISH CRUSTACEA. 
with them ; in the male this appendage is very small, but in 
the female it is greatly developed, and the two form a pouch 
in which the eggs are deposited and the young are hatched, 
hence they have been named Opossum Shrimps, from this 
pouch somewhat resembling in use the pouch of the Mar- 
supial animals. 
These Opossum Shrimps are frequently met with in 
countless myriads towards the surface of the Greenland 
Sea. They seldom approach the shore or retire to the 
lower part of the ocean. Otho Pabricius, in his ‘ Fauna 
Groenlandica/^ which is a model for a work of that na- 
ture, has described three species ; two of these (. Mysis pe~ 
datus and M. oculatus) called Illmrak and Irsitugah by the 
Greenlanders, small though they be, form the chief part of 
the food of the common Whale (Balcena mysticetus). As 
he remarks (p. 33), it is, at the first thought, truly wonder- 
ful that so large an animal should be supported and acquire 
so much fat from so slender and trifling a subject ; but 
when one reflects on the abundance of them being so great 
that the Whale, when it opens its mouth, must draw in 
many thousands at a gulp, the wonder is diminished. The 
little shrimps seem to play about the fringes of the “ whale- 
P. 245. 
