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 Craniate excepting the Cyclostomes. 



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

 tive cartilaginous capsules, and their influence on the process of 



adf 



rns 



IMC. 13. 



Auditory labyrinth of Chiniacra monxt rosa, L. A, inner view ; ]{, outer view. (After 

 Retzius, from Gegenbaur, Vergl. A mat. H'irbeltieiv.) a, auditory nerve ; aa, iifi, (>r, ampullae; 

 ode, opening of ductus ; CM, anterior, c.p, posterior, and it, horizontal .semicircular eaiial : <:><.-; 

 canalis utriculo-saccularis ; D.c, ductus endolymphaticns ; m.n, macula neglecta ; w.s, macula 

 saceuli ; m.n, macula utriculi ; pi, process of macula sacculi ; w, recessus utriculi ; .-, 

 sacculus ; s.tt, sinus utriculi ; , utriculus. 



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

 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- 



