450 OTOLITHS. COENEA. [BOOK I. 



Crystalline fine pulverulent otoliths which occur in most 



appearance animals present the appearance of microscopic crystals, 



of puiveru- presenting remarkable variations in size. Their form 



lent otoliths. ^ g s ] iewn i n the accompanying illustration. 



FIG. 61. OTOLITHS, COMPOSED OP CALCIUM CAKBONATE. (From Frey, after Funke.) 



According to Dahnhardt 1 otoliths contain from about 74'5 to 77'5 

 per cent, of mineral matter, composed chiefly of calcium carbonate in 

 the form of crystals. The organic matter resembles mucus. 



The membranous Labyrinth. 



As yet no information whatever is possessed in reference to the 

 composition of the walls of the labyrinth. Mainly these are com- 

 posed of connective tissue, which is said to resemble the cornea in 

 structure 2 . Of the chemical characters of the epithelium of the 

 labyrinth nothing whatever is known. 



SECT. 2. THE TISSUES AND MEDIA OF THE EYE. 



The Cornea. 



The ground-substance of the cornea presents, as has already been 

 pointed out (p. 271), very great similarity in chemical composition to 

 that of hyaline cartilage, and until lately it was asserted without 

 contradiction that both tissues, when subjected to prolonged boiling, 

 yield chondrin, although that substance, as obtained from the cornea, 

 was said to possess somewhat special reactions. As we have already 

 pointed out, Morochowitz 3 denies the existence of chondrin and looks 



1 Dahnhardt, "Endolymphe u. Perilymphe." Arbeit, d. Kieler physioL Institiits, p. 

 106. 



2 Hensen, Op. cit. p. 68. 



3 Morochowitz, "Zur Histochemie des Bindegewebes." Separat-Abdruck aus den 

 Verhandlungen des naturhist.-med. Vereins zu Heidelberg. Vol. i. Part 5. 



