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 S&pia 

 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. 



