10 BULLETIN OF THE 



the diagonal band in the lobster is materially different from the trans- 

 verse baud in Penseus, and I conclude that in the cornea of the lobster 

 the limiting and diagonal bands are essentially similar in that they both 

 extend through the cuticula. 



In all probability the bands between the facets were produced during 

 the secretion of the cuticula by the interference of the partitions which 

 separate the hypodernial squares. If this be true, it is probable that 

 the diagonal bands represent a lil;e interference. It is important to 

 notice that the diagonal band in the cuticula corresponds to the imagi- 

 nary diagonal which lies between the nuclei of each hypodermal square, 

 never to the diagonal which crosses the nuclei (compare Figs. 2 and 3). 

 This diagonal then corresponds to the position in which one woidd look 

 for a membrane between the pair of hypodermal cells ; and although 

 such a structure has not been observed, the diagonal band in the cornea 

 is a strong indication of its presence. 



Admitting this to be the significance of the diagonal band, it is but 

 natural to expect tliat, if deeper cells touch the cuticula, they would pass 

 outward between the hypodermal cells. The fiict that the hazy patch 

 which lies in the middle of the facet is always on the diagonal band, 

 and directly external to the distal tips of the cone-cells, leads to the 

 belief that this patch marks the place where the cone-cells pass between 

 the cells of the hypodermis and touch the cuticula. I am not of opin- 

 ion that the patch is produced by the secretion of the cone-cells, al- 

 though I have no evidence that the cone-cells cannot produce cuticula 

 at their distal tips. It seems to me more probable that they have given 

 rise to the patch by a series of interrupted interferences with the ac- 

 tivity of the corneal hypodermis. If such be the case, a distinct cross 

 might be produced when the area of interference was definitely circum- 

 scribed. AVhen the area was not so sharply bounded, a hazy patch with 

 indistinct outlines might be the result. 



From the facts which have been presented, I conclude that each hypo- 

 dermal square consists of two flattened cells, triangular in outline, and 

 very intimately applied on their longest sides. 



The Cone-cells. 



One of the most important questions in the anatomy of the cells of 

 the crystalline cones (retinophorse) concerns the relation which these 

 cells bear to the rhabdome. ]\Iax Schultze was the first to maintain 

 ('67, p. 407) that the cone-cells and rhabdomes were separate struc- 

 tures, f^renacher's researches lead to the same conclusion. As an oppo- 



