THE CEPHALOPODA. 



453 



In the Dibranchiata^ the auditory sacs are lodged in cavi- 

 ties of the cephalic cartilage, and contain a single large 

 otolith, composed of carbonate of lime, and of rounded or 

 irregular but definite and characteristic form. In Nautilus^ 

 Dr. Macdonald discovered that the auditory sacs are attached 

 to the pedal ganglia, and are not lodged in the cranial cartilage. 

 They contain numerous otoliths. 



An endoskeleton formed of true cartilage is developed in 

 the region of the principal ganglia, and sometimes furnishes 

 them with a complete investment. It gives attachment to the 

 most important muscles. In some Cephalopods additional 

 cartilnges appear in the mantle and in tlie funnel. The mus- 

 cular fibres of the Cephalopoda are unstriated. 



The sexes are distinct, and the reproductive organs are un- 

 like those of other Mollusks. They consist, in both sexes 

 (Fig. 129), of lamellar or branched organs, the cellular con- 

 tents of which are metamorphosed into ova or spermatozoa, 



ov ^ 



Fig. 129.— 5e/)/a officinalis.— I. male organs: t. testis ; vd. vas defereni=; vs, vesicula 

 seminalis : pi\ prostate ; hsp, receptacle of the spermatophores ; p, penis with the 

 pctiital aperture. (After Duvcmoy.) 



II. Female erenital orL^ans : a. anus ; i, intestine; o?\ ovary ; od'. oviducal aperture; 

 od. oviflncal gland ; gn, nidamental gland ; gn'^ accessory glands. (Alter Milne- 

 Edwards.) 



and which are attached to one point or line of the wall of a 

 chamber, which communicates with the pallial cavity by two 



