SENSE OKGANS OF AMIURUS, 261 



moveable, being attached to the style-like superior maxillaiy bones, 

 and indebted for their nervous supply chiefly to the Br. maxillares 

 V., although they also receive branches from the Br. mandibulares. 

 Attached to the under- surface of the mandible are the four ' mandi- 

 bular ' barblets, supplied by the Br. mandibulares V. 



If the tip of one of the barblets of a young specimen be examined 

 in the fresh condition the end buds are visible both from the surface 

 and in profile. From the latter point of view the organ almost in- 

 variably appears to have a mouth (owing to the retraction of the 

 central zone of the neuro-epithelium), and this appearance is general 

 also in sections of hardened specimens. Leydig, who has observed 

 this phenomenon, attributes it to contractility on the part of the 

 peripheral zone of cells. From the surface view it is easy to distin- 

 guish the two zones of the neuro-epithelium, and likewise in sections 

 which pass transversely to the end-buds. The central cells, which, as 

 distinguished from those of the mantle or periphery, are the sensory 

 elements, occupy the whole length of the end-bud. Difference in 

 form in end-buds from various regions appears to be largely due to 

 the bases of the peripheral cells, which . sometimes are considerably 

 swollen round about the nucleus, at others remain slender even 

 there. On the barblets the end-buds are almost cylindrical in form, 

 and are crowded especially towards the tips. In a hardened speci- 

 men where the interpapillary epidermis is 200 i± thick, the cylindrical 

 end bud extends through 120 /jl, the papilla occupying the rest of the 

 thickness. The transverse diameter of the end-bud at its mouth is 

 17 /x, and each end-bud is separated from its neighbour by about 

 twice its width. In young specimens the end-buds are even more 

 crowded, and stand out even more strongly than in the adult from 

 the rest of the barblet, for the interepithelial pigment cells form a 

 complete and close net work in the young, but afterwards become 

 scattered in the adult. The pigment cells do not encroach upon the 

 end-buds whence, apart from their form, their isolation of the latter 

 from the rest of the epidermis. 



In other regions the cylindrical form gives place to elongated oval 

 or pyriform shapes. Elsewhere the same length is not attained as 

 in the barblets, although the transverse diameter may be consider- 

 ably greater. 



