LATERAL CANAL SYSTEM OF SELACHIANS 7 



Positive observatioRvS in reference to histology and especially 

 those showing nerve terminations are limited in number. But 

 it has been repeatedly shown since Schulze's papers of 1861 and 

 1870 that pear-shaped and club-shaped sensory cells with cutic- 

 ular hairs or bristles are characteristic of the sense organs of the 

 canal system. The sensory cells of the sense-hDlocks are central 

 in position, do not extend to the basilar membrane and are in- 

 termingled and surrounded by long, usually slender, supporting 

 elements extending from the basilar to the limiting membrane. 

 Cells of this kind have been figured with more or less detail by 

 Langerhans '73, Salamandra maculosa, good; Malbranch '76, 

 several amphibians; Solger '80, a nerve plexus in teleosts; Boden- 

 stein '82, Cottus gobio; Mauer '92, fishes and amphibians in- 

 cluding Acanthias and Triton; Kingsbury '95, Diemyctylus, 

 Nectorus; Heilig '12, Kaulbarsch, shows nerve terminations; 

 Pf tiller '14, Macruridae. 



A number of observers from Leydig '50 onwards have pub- 

 lished figures of the specific nerve of the sense organs traced to 

 the basilar membrane without showing nerve terminations. 

 Among the early ones are Allis '88, Maurer '92, etc. But the 

 vexed question of the nerve terminations has proved elusive. 

 Retzius '92 supplied good figures of nerve terminations of end 

 bulbs of fishes and amphibians. Bunker '97 makes definite 

 statements without illustrations of the nerve terminations in 

 Amieurus nebulosus. Heihg '12, gives the best figures and the 

 best summary for the Kaulbarsch (Acerina cernua) and Pfiiller 

 '14, .shows ganglion cells and some fibers in the sense organs of 

 the Macruridae. 



The papers of Bunker, Heilig and Pfiiller require separate 

 mention. 



Bunker '97, by using several methods including haematoxyJin 

 stains, Golgi and methylen-blue, worked out the histology of 

 the nerve cells and of the nerve terminations. It is greatly to 

 be regi'etted that his clear descriptions are not accompanied by 

 sketches. He finds the usual pear-shaped hair-cells in the super- 

 ficial half of the organ. The nerve at the base of the organ 

 consists of 10 or 20 medullated fibers which lose the medullary 



