C. 0. WHITMAN, A Sketch of the Structure and Development of the Eye of Clepsine. 617 



script. The author dismisses my statements summarily, and goes so 

 far as to assert that they have no foundation. ,,Thin serial sections 

 and maceration-preparations" do not disclose any tactile cells in con- 

 nection with the eye, „die Angaben Whitman's müssen daher 

 wohl auf Irrthum beruhen" ! 



My positive statements about the development of the eye are 

 also disputed, although the author confesses to having made no obser- 

 vations on this point. A theory of the development is put forward 

 without so much as a single fact of development to support it; and 

 this theory happens to be all wrong from beginning to end, as I shall 

 show by facts easy of demonstration. 



DcYelopment of the Eyes and the Metameric Sensillae. 



As long ago as 1887 (in : Journal of Morphology, vol. 1, p. 159), 

 it was pointed out that the eyes arise as „bulb-like thickenings of 

 the epidermis", and in the work above cited (p. 590) the origin and 

 differentiation are described thus: „Both the eyes and the 

 segmental sense-organs develop as local thickenings 

 of the epidermis. At first the cells are alike in form, 

 size, and structure. About the time the pigment be- 

 gins to appear, the two sorts of sense-cells begin to 

 show a difference in size, and an indistinct boundary 

 line appears between them." 



These statements were based on a thorough investigation of every 



rSèTd 



V jy 



Fig. A. Sagittal section of a young Clepsine plana, about 2 mm in length, showing 

 the head, ^280. / — V Segments marked by sense organs in process of formation. 



