SENSE-ORGANS 



complicated folding of this sac are elaborated a sacculus and 

 utriculus, from which spring two vertical and one horizontal 

 semicircular canals in all Craniata excepting the Cyclostomes. 



The relation these organs of special sense bear to their respec- 

 tive cartilaginous capsules, and their influence on the process of 



ade 



ms 



Fio. 13. 



Auditory labyrinth of Cldniaera mon*tro*a, L. A, inner view ; H, outer view. (After 

 Retzius, from Gtegenbaur, Vergl. Anat. Wirbelticre.) a, auditory nerve ; ua, op, ae, ampullae; 

 ade, opening of ductus ; CM, anterior, c.p, posterior, and cc, horizontal semicircular canal ; .-.*, 

 eanalM utnculo-saccularis ; D.e, ductus endolyniphaticus ; m.n, macula neglecta ; m.s, macula 

 sacculi ; m.w, macula utriculi ; pi, process of macula sacculi ; rec, recessus utriculi ; .<, 

 sacculus ; s.u, sinus utriculi ; /, utriculus. 



cephalisation, has already been alluded to above (p. 2). No honio- 

 logues of these organs have been found in the Cephalochorda. 



Yet another organ of sense remains to be noticed the pineal 

 eye. Although it may not have a claim to the all-important 

 function attributed to it by Descartes, the pineal eye, or epiphysis, 

 is of considerable interest. Leydig in 1874 described it as a sense- 

 organ ; but De Graaf and Spencer, in 1886, were the first to demon- 



