LATERAL CANAL SYSTEM OF SELACHIANS 9 



figures of Macrurus fastiatus and M. cavernosus are shown 

 small ganglion cells at the base of the sense organ and also with- 

 in the region of the epithelium. So far as I have been able to 

 determine nothing of this kind exists in Mustelus and Squalus. 

 The relatively small size of his 'ganglion cells' is in marked 

 contrast with the large nerve fibers of the ner\ais lateralis and 

 of the far removed ganglion cells of the selachians. 



III. MATERIAL, METHODS AND TERMINOLOGY 



The material available for this investigation consisted of a 

 large number of Squalus acanthias embryos ranging from the 

 open neural groove stage to small adults (garters), and Mustelus 

 canis adults and pups, and a few rather poorly preserved em- 

 bryos of this species between 26 mm. and 80 nmi. in length. 

 Squalus embryos between 36 mm. and 72 mm. were not plenti- 

 ful and there were none between 72 mm. and 180 mm. The 

 vSqualus material had been fixed in the usual reagents and pre- 

 served in alcoholic and formalin solutions. Fresh Mustelus 

 adults and pups were secured at the Marine Biological Labora- 

 tory, Woods Hole, Mas.sachusetts. 



Only a few words need be said concerning the methods em- 

 ployed. With preserved material iron haematoxylin gave the 

 best results for sections. No success attended my efforts to 

 secure silver impregnation of the peripheral nerve terminations 

 of preserved specimens. The binocular dissecting microscope 

 was found to be indispensable in dissecting and studying the 

 distribution and ner\'e supply of the sensory thickenings in 

 early embryos. 



With fresh Mustelus material, good impregnations of the 

 peripheral nerve terminations were obtained. Several modifica- 

 tions of the Ramon y Cajal method gave fairly good results, 

 but the best preparations were obtained by a slight modification 

 of the silver-pyridine method introduced by S. W. Ranson. 



The modification I found most successful may be outlined as 

 follows: Fresh specimens are decapitated, and narrow strips of 

 integument containing the sensory canals desired are rapidly 

 removed, cut into short sections, rinsed briefly in distilled water, 

 drained on blotting paper, and put into a large volume of ab- 



