THE WEBBED SEPIA. 503 
is to cover the shell on its exterior, and, as has since been definitely proved, to 
build up its delicate texture and to repair damages, the substance ot the shell 
being secreted by these arms, and by their broad expansions mouldedinto shape, 
‘The modes of progression empioyed by the Argonaut are to the full as 
wondrous as its fabled havits of sailing. Its progression by crawling has 
already been casually mentioned. While thus engaged, the creature turns 
itself so as to rest on its head, withdraws its body as tar as possible into its 
shell, and, using its arms like legs, creeps slowly but securely along the 
ground, sometimes affixing its discs to stones or projecting points of rocks 
for the purpose of hauling itself along. 
When, however, it wishes to attain greater speed, and to pass through the 
wide waters, it makes use of a totally different principle. 
As has already been mentioned, the respiration is achieved by the passage 
of water over the double gills or branchiz ; the water, after it has completed 
its purpose, being ejected through a moderately long tube, technically called 
the sipnon. The orifice of the siphon is directed towards the head of the 
animal, and it is by means of this simple apparatus that the act of progression 
is effected. When the creature desires to dart rapidly through the water, it 
WEBBED SEPIA.—(Cirrhoteuthis Multert.) 
COMMON SEPIA.—(Sepia officinalis.) 
gathers its six arms in a straight line, so as to afford the slightest possible 
resistance to the water through which it passes, keeps its velated arms 
stretched tightly over the shell, and then by violently ejecting water from 
the siphon, drives itself, by the reaction, in the opposite direction. 
As the various cephalopods are so numerous as to preclude all possibility of 
figuring and describing each species, we must therefore content ourselves 
with a typical form of each family and a general account of its members. 
The lower figure in the illustration represents the common SEPIA of our 
