46 
Tanks 7 and 11. 
over the sand like a swarm of flies. These are not the young of some 
larger shrimp, but fully grown animals, the Opossum-shrimps or Mysi- 
deae. They are remarkable for having their organ of hearing quite 
in their tails, and each leg terminating in two prongs. The higher 
forms of crabs have such "bifid” feet at the earlier periods of their life 
Fig. 73. Eriphia spinifrons, % nat. size. 
and have probably sprung from some form similar to the Mysideae 
of to-day. 
Out of the group of the Isopoda (of which the wood-louse is a typical 
example, being an Isopod which has taken to terrestrial life) visitors 
may often see the parasitic forms Anilocra and Cymothoa (Fish-lice) 
Fig. 74. Squilla mantis, ! /2 nat. size. 
fixed to various fishes. They are attached to the head, the eyes, and 
the tail of the fish by means of their mouth-appendages and the sharp 
sickle-shaped legs (7 pairs); or they are attached within the gills or the 
throat of the fish and suck its blood; they may attain the length of a 
couple of inches. They fix themselves so firmly that no endeavours of the 
tortured animal can dislodge them. The females carry about their eggs 
in a special brood-pouch, on the under surface of their body, till the 
young ones are hatched. A curious fact worth noticing is that all females 
have in their youth been males; the new born animals are not divided into 
the two sexes but, figuring as males in their early life, when they have 
grown older they take upon themselves the duty of producing eggs. 
