No. 4.] 



AMPULLAE OF THE SELACHII. 



167 



mens, one a female 1.07 m. long, the other a pup 26 cm. long. 

 The following are the results of my computation : 



In supra-orbital-buccal groups 



In right hyoid group . 



In left hyoid group 



In right mandibular group . 



In left mandibular group 



Totals 



'595 



1458 



On comparing the two columns of figures it will be seen 

 that the number of ampullae probably does not increase 

 after the birth of the fish, as in some groups 

 the number is larger in the pup. The dif- 

 ference in the total number is probably due 

 to individual variation. 



The ampullae are imbedded in a matrix 

 of clear gelatinous tissue, through which 

 run the nerves supplying these organs. 

 The whole mass is surrounded by fibrous 

 connective tissue which is pierced by the 

 tubes as they run out from the ampullae. 



Gross Anatomy of an Ampulla. - - At its 

 inner end each ampullary tube from the 

 surface opens into one of the so-called 

 ampullae of Lorenzini (Fig. I, a.). Viewed 

 from the side an ampulla is seen to be a 

 sac more or less spherical in form, with 

 slight outpocketings (Fig. I, a.pkt.} which 

 vary in number from eight to twelve. If 

 one looks at the proximal end of the am- 



11 .1 i 11 



pulla, the pockets are clearly seen as a 

 circle of protuberances. The internal 

 structure is best made out when the am- 

 pulla is sectioned transversely in a plane 

 just above its largest diameter. Looking into the organ one 

 sees the out-pocketings noticed on the outside, while partitions 

 also appear running from the divisions between these pockets 



FIG. i. Outline drawing of 

 tube and ampulla: a., am- 

 pulla; a. ., ampulla nerve ; 

 a.p., ampulla surface pore ; 

 a.pki., ampulla pocket; 

 a.t., ampulla tube. x 12. 



