216 THE POPULAR SCIENCE MONTHLY 

ONE OF THE Happy FAMILIES IN THE AQUARIUM. 
erated. The semi-transparent squids, with posterior triangular fins, 
swim back and forth as delicately poised as submarine monoplanes. 
When a live fish is placed in the water the squid darts at it, grasps it 
firmly with the suckers or the tentacles and cuts off the head, eating 
only the body. The cuttlefish, with broader body, striped like a zebra, 
and big elephantine head, constantly undulates a fin-like fringe around 
the border of its mantle, as it nervously drifts here and there. Fre- 
quently it wriggles into the sand which it throws upon its back, or, 
if much disturbed, ejects a cloud of ink in which it disappears. The 
large octopus has a body that suggests both a toad and a spider, with 
highly developed eyes and brain projecting above it. Generally this 
devil-fish lies sleeping in a corner of the rocks, or lazily reaching out 
and creeping about by means of eight long tentacles that express a 
giant’s strength. With a spurt of water from its siphon the octopus 
may dart rapidly through the tank, and by directing the tube of its 
siphon, go whither it wills. Lying upon the bottom of an open trough, 
often buried in the sand, is the very interesting electric ray. If one 
presses the fingers upon the broad body where it runs into the tail he 
will, in the words of a Cook’s guide, “ get a strike.” The electric tis- 
sues are descended from muscle fibers which in the course of evolution 
have come to produce electricity instead of motion. In the embryo 
ray the primitive muscle cells first appear, then they swell out anteriorly 
and shrivel up posteriorly until each loses the characteristic striated 
muscle structure and becomes an electric plate lying in a little com- 
partment embedded in a jelly-like substance. Electricity is produced 
by some chemical action upon innumerable minute granules stored up 
in the protoplasmic network pervading the electric plates. The shock 
