ANATOMY OF LOLIGO. 277 



short muscular canal with a large orifice extending on 

 the ventral side to the base of the tentacles. Through 

 this siphon passes excrementitious matter as well as the ink, 

 and the stream of water which is forcibly ejected from the 

 siphon, thus propelling the squid through and sometimes 

 out of the water. 



The two gills (Fig. 213, g), are large, long slender bodies, at- 

 tached by a thin membrane to the inner wall of the mantle, 

 and are quite free from the visceral mass. From the bran- 

 chial vein arise two rows of lamellae like the teeth of a comb. 

 At the base of each gill is a flatted oval body, the " bran- 

 chial heart," or auricle (Fig. 213, bh). The auricles are quite 

 separate from the large four-cornered flat ventricle (Fig. 

 213, h), lying in front of the stomach, and which throws off an 

 artery from each corner, the aorta being the largest, and 

 passing parallel to the oesophagus, while a large vein (vena 

 cava) is sent off to the gills from a circular sinus in the 

 head. 



The nervous system is more complicated than usual in 

 Mollusca, and is very difficult to dissect. In Loligo Pealii the 

 highly concentrated nervous system is mainly contained in an 

 imperfect cartilaginous brain-box (eg), a slight anticipation of 

 the skull of the Vertebrates. The brain (supraoesophageal 

 ganglion, Fig. 213, cl) rests upon the very large optic nerves, 

 which dilate at the base of the eye, the latter being partially 

 imbedded in sockets in the brain-box. The visceral (parie- 

 tosplanchnic) ganglion lies beneath and a little behind the 

 brain, supplying the nerves for the ears (otocysts), which 

 are enclosed in the cartilaginous brain-box, and there is a fine 

 canal leading from the ears to the surface of the body, so 

 that, as Gegenbaur states, it is possible to distinguish a mem- 

 branous and a cartilaginous labyrinth, analogous to the 

 similar parts found in the Vertebrates. The pedal ganglion 

 (Fig. 213, p) is paired with the visceral ganglion (Fig. 213, r), 

 but lies in front of it, behind and under the bulbous pha- 

 rynx, and from it arise ten nerves (t), which are distributed one 

 to each arm, passing between the two rows of suckers. Two 

 smaller ganglia, the superior buccal and inferior buccal, lie 

 one above and one below the beginning of the oesophagus. 



