106 PROC. ENT. SOC. WASH., VOL. 20. NO. 5, MAY, 1918 



while in a normal specimen the median eye has a diameter of about 

 0.353 mm. The lateral ocelli are circular and of approximately 

 normal size. 



The antennae (fig. 1 are of normal size, consisting of 13 seg- 

 ments and in every respect conform to the normal type. The 

 mouth parts show no notable deviation from the normal, although 

 they seem unusually conspicuous. This feature is however due to 

 the relatively small size of the head. 



Examination of a series of transverse sections of the head fails to 

 reveal the slightest vestige of the compound eyes. On comparing 

 these sections with a similar series of the head of a normal drone it 

 is evident that the central portion of the brain is of approximately 

 normal size. Figures 3 and 4 represent two sections through the 

 brain of the abnormal drone, the section shown by figure 4 being 

 anterior to that shown by figure 5. The mushroom bodies (MB) 

 are apparently of normal size and form, although in the abnormal 

 drone the two calices of each side lie more nearly in the same trans- 

 verse plane than in the normal drone, being in this respect more 

 like those of the worker bee. The most important and striking 

 feature of the brain of the abnormal drone is the almost complete 

 absence of the optic lobes. In the abnormal drone the parts 

 wanting are those termed by Hickson the "periopticon" and "epi- 

 opticon." The "opticon," including the inner fibrillar mass, is 

 present, but in a reduced condition, as seen in figures 3 and 4, 

 IFM. Moreover the inner fibrillar mass of the left side (right in 

 the figures) is situated further cephalad than that on the right side. 

 Over both of these the neurilemma extends in an unbroken layer. 



In regard to the cause of the loss of the eyes and the accompany- 

 ing parts of the optic lobes there is little to be said. The com- 

 pleteness of their absence argues against mechanical injury, more- 

 over this is also rendered improbable by the protected environ- 

 ment of the developmental stages. It is necessary to conclude 

 therefore that the abnormality is referable to a deficiency in the 

 germ of the determining factors for the parts lost, whatever this 

 deficiency may be. 



Normally eyeless insects, such as the termites, are of course 

 sufficiently well known. In this connection may be mentioned 

 the cave-inhabiting carabid beetle Anopthalmus, in which, accord- 

 ing to Packard 1 the optic lobes as well as the eyes are completely 

 wanting. Cheshire 2 describes and figures an eyeless drone quite 

 similar to the one described above but differing from it in that the 

 occelli are also wanting and the vertex of the head is concave 1 in- 



1 Packard, A. S. A Text-Book of Entomology. New York, 1909, p. 241 . 



2 Cheshire, Frank R. Beekeeping, Scientific and Practical. Vol. 1. 

 London, 1886, p. 117. 



