220 ZOOLOGY 
certain special sense cells, each provided with a single sense 
hair. This organ is supplied by a nerve which arises from a 
special ganglion situated near the base of the optic ganglion. 
No osphradia corresponding with those of other Molluscs have 
yet been described in Sepia. 
Certain large cells crowded with pigment, situated in the 
subepidermal connective tissue, play an important part in the 
life of a Cephalopod. Attached to these cells, which are called 
chromatophores, are a number of radiating muscle fibres; when 
these contract, the cavity of the cell enlarges, and the contained 
colour becomes diffuse; the chromatophores contract by their 
own elasticity, and when contracted the colour is concentrated. 
The whole system is under nervous control, and the colour of 
the animal may change with startling rapidity In the Sepia 
and other members of the group this faculty is used as a pro- 
tection, the colour of the animal tending to assimilate itself to 
that of the surrounding rocks or sand. In addition to the 
chromatophores, the subepidermal tissues contain other modified 
connective tissue cells known as iridocysts; these cells are so 
modified as to produce iridescent colours by the diffraction 
of light. 
Sepia is a dioecious animal which lays eggs. The male is 
usually somewhat smaller than the female, and its arms are 
relatively longer; the fifth arm on the left side is hecto- 
cotylised, that is, it is modified in connection with the process 
of depositing the spermatozoa. It is thickened at its base, 
and almost devoid of suckers. The testis lies at the extreme 
end of the visceral hump, in a capsule—part of the coelom— 
into which opens a more or less coiled vas deferens, the 
walls of which are much folded, and provided with numerous 
glandular diverticula. Whilst passing down this vas deferens 
the spermatozoa are divided up into packets, and_ the 
glandular walls secrete around each packet a_ cuticular 
spermatophore. Finally, the sperm duct opens into a large 
receptacle known as Needham’s sac, in which the spermatophores 
are stored up; they pass to the exterior by the genital pore 
situated to the left of the anus, and they are deposited in the 
hectocotylised arm, and are possibly introduced by it into the 
mantle cavity of the female at the time of oviposition. 
