200 LANGDON. [Vol. XL 



generally appear elliptical in longitudinal section; some have a 

 truncated top, and a few have one side concave. In a cross 

 section of a nucleus it appears elliptical, circular, or almost 

 triangular. In each nucleus several large nucleoli and usually 

 a few chromatin threads can be made out. The nuclei of the 

 sense-cells cannot be distinguished from those of the support- 

 ing cells. 



Over each sense-organ the cuticula is elevated and much 

 thinner than elsewhere. These two features render it concave 

 on the side next to the sense-organ, and convex on the outer 

 surface. In longitudinal sections through a sense-organ, the 

 fine canals through which the sense-hairs pass may be easily 

 seen piercing this place in the cuticula. When the sense-cells 

 are straight and their upper parts quite slender, the hairs show 

 plainly above the cuticula ; but when the upper parts of the 

 sense-cells are thickened or thrown into sinuous curves, the 

 hairs are found to be partly or wholly withdrawn into the 

 cuticular pores. This sinuous appearance is often seen in 

 alcoholic material, and may be accounted for in two ways : the 

 gradual stupefaction of the worm in alcohol may cause a con- 

 traction of separate portions of the protoplasm instead of an 

 even contraction of the whole cell, or there may be first an 

 even contraction, and afterwards a relaxation of part of the 

 protoplasm. When a sense-hair is drawn into its canal, the 

 part which normally lies in this canal is below the cuticula. 

 This part is then seen to be of the same finely granular proto- 

 plasm as the part of the cell below it, and it generally shortens 

 and widens. This contraction of the sense-cells and with- 

 drawal of their hairs into the pores in the cuticula may be a 

 normal process in response to external irritation, but is proba- 

 bly an unnatural contraction caused by the alcohol. The more 

 delicate nature of the sense-cells and their comparative free- 

 dom from contact with each other permit reagents to act on 

 them to a greater extent than on the other epidermal cells. 



In these haematoxylin preparations, bundles of lightly stained 

 fibres are found passing through the circular muscle-layer and 

 pressing against the basement-membrane of the epidermis. 

 Each bundle is enclosed in a nucleated membrane and its 



