246 MORPHOLOGY OF INVERTEBRATE TYPES 



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foot. Altogether the squid has fifteen paired and one single 

 ganglion. The latter is the splanchnic ganglion. It supplies 

 nerves to the alimentary canal and is connected with the so- 

 called infrabuccal ganglia which are in turn connected with the 

 cerebral and pedal ganglia. 



Two large eyes are situated on the head, each in its own 

 capsule. Each is connected with its optic ganglion by a short 

 optic nerve. The structure of the eye is very similar to that of 

 the vertebrate eye. The eyeball is provided with nine eye- 

 muscles. The outer chamber of the eye communicates with 

 the outside by means of the aquiferous pore situated imme- 

 diately beyond the edge of the cornea. The iris is thick and 

 iridescent. A small contractile fold of it projects, when in the 

 light, so as to give the pupil the shape of a crescent. The spheri- 

 cal lens is attached to the ciliary body by a sheet of connective 

 tissue and is brought nearer to or farther away from the retina 

 by the ciliary muscle. The retina is direct. Wedged in between 

 the eyeball and the optic ganglion, on each side of the head, are 

 two lymphatic glands the so-called white bodies. 



The two olfactory crests harbor in their concavity a special 

 sense organ possibly with olfactory function. They receive 

 their nerves from the pedal ganglion. 



Two statocysts are situated in the cephalic cartilage below 

 the visceral ganglia. Each statocyst consists of a cavity lined 

 with epithelium. Twelve papillae project into the cavity. In 

 one place the epithelium is ciliated and forms the macula statica 

 on which the statolyth rests. A ciliated ridge crista statica 

 winds along the walls of the cavity. A ciliated canal Kolliker's 

 duct leads from the cavity toward the surface. The duct ends 

 blindly in the adult squid, but communicates with the outside 

 in the embryonic stages. The statocysts receive their nerve 

 supply from the pedal ganglia in the shape of two eristic and 

 two macular nerves. 



Organs of taste are found on the tongue or ligula. They 

 receive their nerve supply from the infrabuccal ganglia. 



