196 P. G. HEATHCOTE. 



folds and irregularities into which it is thrown (fig. 5, hy.). 

 Their nucleus is larger and stains more deeply. At the lateral 

 Ventral lip (fig. 2, Ivl.) the cells are more elongated and more 

 closely packed together, and gradually take the character of 

 the sensory epithelium which forms the greater part of the 

 lining of the pouches. These sensory cells are long and 

 columnar and at their outer ends are prolonged into a blunt 

 projection of less diameter than the rest of the cell (fig. 7, oe.) 

 and about one third the length of the whole. At the folds 

 which bound the median recess the cells lose their sensory 

 character and take the form of the ordinary hypodermic cells. 

 The mass of sensory cells at the top of the median recess which 

 are continuous with the hypodermic cells are of a character 

 distinct from those described as lining the pouches. They are 

 of irregular elongated shape and resemble ganglion-cells, the 

 inner end being sometimes bifurcated (fig. 6, Bi.). The sensory 

 epithelial layer is of considerable thickness (fig. 2). 



I have hitherto spoken of the epithelial layers simply as in- 

 Testing the chitinous pouches with their hairs, but 1 will now 

 consider the means by which the hairs and cells come into 

 relation. There is no doubt that the terminal parts of the 

 sense cells project into the depressions (fig. 3) in the chitin, 

 caused by the folds spoken of above, and that each chitinous 

 hair is inserted into the chitin immediately outside this pro- 

 jecting part of a sense cell. I am also inclined to believe, 

 though, owing to the small amount of material at my command 

 my evidence on this point is not conclusive, that the bases of 

 the chitinous hairs, i. e. the part which projects on the inner 

 side of the chitinous lining, have a small cavity in their basal 

 parts, into which a threadlike prolongation of the sense cell 

 projects. 



I have invariably found foreign bodies in the median and 

 lateral recesses, and as the latter are in coftimunication with 

 the exterior they may possibly be grains of dirt or sand, but 

 I think that they may be concretions. 



