MORPHOLOGY OF COMPOUND EYES OF AETHROPODS. 143 



On the Morphology of the Compound Eyes of 

 Arthropods. 



By 



S, ITatase, 



Fellow of the Johns Hopkins University. 



With Plate XIX. 



Prefatory Note. — The following extract and accompanying plate, from a 

 memoir recently published in the ' Studies from the Biological Laboratory, 

 Johns Hopkins University,' vol. iv, are here reproduced because it seems to 

 me that they form a very important contribution to a subject which has 

 been largely discussed in the pages of this journal, whilst they may not be 

 readily accessible to European morphologists. In Mr. Watase's original 

 paper a description and figures of the structure of the lateral eyes of 

 Limulus, and of the compound eyes of other Arthropods, are given; but the 

 diagrams in the plate now reproduced are sufiBcient to indicate the author's 

 conclusions. 



The distinctive feature about Mr. Watase's views is that he does not, as I 

 did in my paper published conjointly with A. G. Bourne, on the "Eyes of 

 Scorpio and Limulus," ' Quart. Journ. Micr. Sci.,' vol. xxiii, endeavour 

 to derive the compound eye of Arthropods from a segregation of such dip- 

 lostichous eyes as the central eyes of Arachnida ; but, leaving these entirely 

 aside, derives the commoner type of Arthropod compound eye from the 

 monostichous lateral eyes of Limulus. 



This seems to me to be a very happy suggestion. At the same time, I 

 regret that the author has not, apparently, accepted the statements made by 

 Bourne and myself as to the simple monostichous structure of the lateral eyes 

 of Scorpions — nor investigated their structure for himself. Had he done so, 

 he would have been able to assign even a clearer and simpler starting point 

 for the " ommatidium " of the compound Arthropod eye than that afforded by 

 the lateral eyes of Limulus, where the anomalous central ganglion-cell dis- 

 covered by him, presents us with a complication. There is, I believe, no 



