24 



a lower pair which passes obUqiiely downward to the middle of the lower 

 surface. At the side of the siphon , but facing downward is the siphonal 

 cartilage , a grooved plate to which many muscle fibres are attached and which 

 tits over the corresponding pallial cartilage. The siphon is attached to the head 

 and liver case by the two siphonal valves and the "bridle." The latter is formed 

 by two pairs of muscles , the siphonal protracters . which arise from the pedal 

 process of the skull and pass outward and backward to their insertion upon the 

 upper surface of the mantle. Each siphonal valve is a rectangular sheet of 

 muscle which is attached by its upper edge to the nuchal cartilage . by its front 

 edge to the liver case and by its lower edge to the siphonal cartilage. The 

 free edge of this valve projects backward and prevents watei' which has entered 

 the mantle chamber between the valve and the collar from escaping again 

 through that opening. Another valve is formed by a muscular plate which 

 projects outward from the innei' surface of the uppei- half of the siphon as far 

 as the end of the sii)hon and which prevents water from entering the mantle 

 chamber through the siphon. The funnel is somewhat flattened to fit the .space 

 between the body and mantle. Its ventral half pi'ojects from the mantle cavity 

 and may be directed forward or backward at will. Because of the presence of 

 the valve in the siphon the expanding mantle draws water in only over the 

 latei'al siphonal vah-es and , because of the closure of the latter valves . expels 

 the water from the pallial chamber only through the siphon. A jet of water 

 from the siphon directed either forward or backward serves t(j propel the squid 

 backward or forward. 



The inner surface of the funnel has two pairs of long , elliptical glands , the 

 siphonal glands, whose structure has been described in connection with the 

 epidermis. The upper glands lie on the bases of the siphonal retractors and 

 unite with one another in front. The lower glands are widely separate and lie 

 upon the lower wall of the siphon. The surface of these glands is visibly 

 elevated above the siphonal wall and is covered with slime. The function of the 

 glands is unknown. 



Muscles in the visceral mass. 



The cephalic and nuchal retractors. The cephalic and nuchal retractors with 

 the nuchal and post-cephalic cartilages which are imbedded in them form a 

 hollow cone or case which contains the liver. The base of this case is attached 

 to the skull, and its apex is attached to the middle of the pen. The cephalic 

 retractor arises pa)'tly from the pen and partly from the nuchal cartilage and is 



