THE ELASMOBRANCH FISHES 



281 



ceptor cells, as hexagonal plates, line the ampulla. They are apparently not 

 provided with hair-like processes which extend into the ampuUary cavity but 

 each pyramidal cell has a sensory nerve (o/.) leaving from the apex of the cell. 

 A motor axone (ef.) extends to 

 each of the secreting or flask-like 

 cells. 



In their development the ani- 

 pnllary organs, like the long ca- 

 nals, form as pits of the epider- 

 mis. These pits sink deeply into 

 the integument and often extend 

 far forward or backward forming 

 more or less elongate tubules. At 

 the end of the deepest part the 

 tubule swells out, forming an am- 

 pulla of Lorenzini. 



The vesicles of Savi found in 

 Torpedo consist of from one hun- 

 dred to two hundred hollow sacs 

 in the region of the nasal pit and 



ventrally between the cartilage of the pectoral fin and the electric organ. 

 Each vesicle is a transformed canal organ which, unlike an ampulla of Loren- 

 zini, is unconnected with the exterior. Such a vesicle is composed of three discs, 

 one of which is large and occupies a median position while at the sides of this 

 are two lateral and smaller ones. 



Pit Organs 



In addition to the above-mentioned organs, pit organs found in sharks and 

 rays may here be descril)ed. These organs were early seen in the rays along the 

 back just mediad of the lateral line and from the suprascapular line to the 



Fig. 248. Section showing ending of nerves (h.) 

 in ampulla. (From Eetzius.) 



Fig. 249. Eeceptor cells and gland 

 cells in an ampulla of Lorenzini. 

 (From Dotterweich.) 



af., afferent nerve ; ef., efferent 

 nerve ; <;., gland cells ; s., sensory cell. 



Fig. 250. Pit organ, Haia l)atis. (From 

 Ewart and Mitchell.) 



first dorsal fin. Others occur along the hyomandilndar and the infraorbital 

 canals in the head. 



Ewart and Mitchell (1891) have given a section through a pit organ of the 

 ray (fig. 250) which shows it to be not unlike a taste bud. The narrow neck 

 leads to a group of sense cells which form a ball. Each of the sense cells is long 



