58 Journal of Comparative Neurology. 



ated cuticula would form a central tube and the peripheral ends 

 of the epidermal cells, being attached to this cuticula, would 

 arch inward to this tube. The surface of the latter would thus 

 be covered with the hexagonal ends of these cells. If now an 

 increase in the depth of the epidermis should take place by an 

 elongation of its cells and if also the nucleated parts of the cells 

 attached to the tube should grow downward and laterally so as 

 to lie among the bases of the other epidermal cells, there would 

 be two forces pulling upon the peripheral ends attached to the 

 central tube. One force would tend to pull the cuticular tube 

 outward away from the cells attached to it ; the other force 

 would tend to pull the peripheral ends of these cells downward 

 away from the tube. If the strain from these two forces con- 

 tinued long enough it would tend to pull the peripheral ends of 

 the cells away from the central tube. As a result of either 

 force it would be the upper part of each process which would first 

 loose its connection with the cuticular tube, because this part 

 is more convex and thus being under a strain due to its own 

 form is less able to resist the downward pull of its own cell-body 

 or the upward pull of the cuticular tube to which it is attached. 

 It will be remembered that, in these organs, there is a space be- 

 tween two adjacent turns of the spiral and that the upper half 

 of the inner face of each component block of the spiral is usu- 

 ally free while the lower half is still joined to the tube. Such 

 a process as that described above would account for both of 

 these — the free upper half of the upper face of the block 

 would be the half of the peripheral end which had been 

 pulled away from the surface of the central tube ; the space 

 between two adjacent turns of the spiral would be the space 

 thus left upon this tube, increased probably by a stretch- 

 ing of the thin cuticular tube itself. It will be remembered 

 that some of these component blocks of a spiral bear ridges 

 upon their upper surfaces while some are smooth. This is prob- 

 ably to be accounted for by the fact that all of the cells in any 

 epidermal area are not true hexagons. In some cases it may 

 also be accounted for by the possibility of some of the refrac- 

 tive blocks being still in a plastic condition when the separation 



