19() THE CANADIAN ENTOMOLOGIST. 



THE "EYE-SPOTS" OF ALAUS OCULATUS. 



BY F. ALEX. MCDERMOTT, WASHINGTON, D. C. 



The large elater, Alaus oculatus^ whose pronotum bears the two large 

 black-and-white eye-spots which give the insect its species name, is a 

 prominent specimen in practically every large collection of Coleoptera in 

 this country \ and if not the oculatiis^ then some of its near relatives, 

 similarly marked, will surely be there. Usually, also, one will find in 

 these collections, the cucuyo, Pyrophorus fioctilucus, or some of its allies, 

 whose thoracic portions bear two spots very similarly situated, but this 

 time of a yellow colour and smaller, and during the life of the insect 

 emitting that remarkable light, which was the basis of the researches of 

 Langley and Very, "On the Cheapest Form of Light. ""^ Those who observe 

 these insects, either alive or dead, would naturally wonder whether the 

 oculatiis might not be luminous, or at least have beneath its chitin some 

 structure indicating that the eye-spots were a degradation of the photogenic 

 organs of the cucuyo. In the matter of classification, the insects are not 

 particularly closely related ; both are elaters, to be sure, but in different 

 subfamilies, and not very strikingly similar in their mode of life. 



The extremely hard chitin of the oculatus renders it a difficult subject 

 for histologic work. However, the idea above mentioned, that there might 

 be some sub-chitinous structure, occurred to the writer some time ago, and 

 in pursuance thereof, he has attempted to gain some knowledge of the 

 structure of these eye-spots. A number of sections have been made by 

 hand, the sub-tissues bemg stained with acid carmine, and the mounting 

 being in paraffin. While the general statement may be made that there is 

 no special organic structure beneath these eye-spots, the observations upon 

 them seem to justify publication, as a matter of interest, inasmuch as no 

 previous paper appears to have been published on this point, so far as I 

 have been able to ascertain, though to my knowledge, others have been 

 interested in this same subject. 



Each spot consists of an elliptical, convex area, whose edge is de- 

 pressed below the surrounding thoracic chitin. Under a low-power lens 

 they appear to be covered with a dense, black pile, like black velvet, 

 while the edge of the spots bears short, coarse white hairs. With higher 

 powers the velvety pile resolves itself a mass of flat, scale-like chitinous 

 hairs, showing a few longitudinal ribs, and slightly concavo-convex. Their 

 general shape under the lens resembles the chaff from grain. The white 

 hairs of the edge are similar, but coarser. Both are hard to remove, and 



* Smithsonian Misc. Coll., No. 1258, Washington, 1901. 

 June, 1911 



