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Howard Ayers and Julia Worthington 
appear at present. They have been found outside of the dermal groove 
as well as within it. 
When instead of skin preserved in formalin, skin of a young hagfish 
that has been preserved in chromic acid is used, startlingly different re- 
sults are obtained. The essential features, the deep surface canal of the 
epidermis, the spindle-celled ridge, the dermal groove, are all present; 
but in addition to these the chromic acid causes the inner epidermal layer 
te separate into two parts along what appears to be a definite line of weak- 
ness, and thus forms closed tubes that appear between the dermal groove 
Fic. 10. Cross-section of skin through lateral line canal of young Bdellos- 
toma, 11 inches long, preserved in chromic acid. b—=basement membrane, 
d=dermis, e—epidermis, g—lateral line canal, m—=mucous cell, n= 
nerve bundle, N = spindle-cell ridge (broken across), s—=single sensory cell, 
¢—tube beneath canal, v —blood-vessel. = 153. 
and the superficial canal (Figs. 8,9, and 10,7). The closed tubes are as 
long as the dermal grooves, and consequently longer than the surface 
canals. Fig. 8 is a typical section of one of these tubes just before its 
end, after passing the end of the canal, and this same appearance is also 
found in the territory of the closed tube in the inter-spaces shown in 
Figs. 5 and 6 in which the surface canal is interrupted. The closed tube 
is, for the most part, separated by only a single layer of small cells from 
the basement membrane. Above the lumen of the tube are several layers 
of small cells before the large celled layer of the epidermis is reached. 
The sides of the tube are usually bounded by long slender cells, and its 
roof, in this section, contains several mucous cells. 
