SENSE ORGANS OF AMIURUS, 261 
moveable, being attached to the style-like superior maxillary bones, 
and-indebted for their nervous supply chiefly to the Rr. mawillares 
V., although they also receive branches from the Rr. mandibulares. 
Attached to the under-surface of the mandible are the four ‘ mandi- 
bular’ barblets, supplied by the Rr. 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 » thick, the cylindrical 
end bud extends through 120 y, the papilla occupying the rest of the 
thickness. The transverse diameter of the end-bud at its mouth is 
17 p», 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. 
