288 
Psyche 
[December 
The first hypothesis to suggest itself, and one that has al- 
ready been advanced to explain this type of malformation, is 
that it may have a phylogenetic significance, and may constitute 
a reversion to an ancestral condition. 
Examining the plausibility of this hypothesis, we find that 
Patten 5 has shown in a late larval or prepupal stage of a wasp, 
that the median ocellus first appears as a pair of separate pits or 
vescicles, which later unite to form a single ocellus on the median 
line. Packarde has stated that in the pupa of a bumble bee the 
median ocellus presents a “double shape, being broad, trans- 
versely ovate, and not round like the two others, as if resulting 
from the fusion of what were originally two distinct ocelli.” 
Leydig , 7 Rabl-Rueckhard , 8 Carriere , 9 Viallanes , 10 Janet, 11 , 
and others have shown that in certain adult Hymenoptera the 
median ocellar nerve is double throughout some part of its 
length, while Burgess 12 in his figure of the brain of the Rocky 
Mountain Locust shows the median ocellar nerve to be unpaired 
in that species; still, in common with all structures located on 
the middle line of an organism having bilateral symmetry, where 
in early segmentation stages the plane of one of the cleavages 
corresponds to the future middle line, the median ocellus must in 
all groups of insects have been double at some point in the 
course of its development in the individual, and the condition 
of this structure in the Hymenoptera might seem to indicate 
that its origin from the fusion of an ancestral pair of ocelli may 
have occurred at no very remote period in the phylogeny of the 
class. 
Indeed, the hypothesis begins to look delightfully plausible 
when only the supporting evidence is considered, but on the 
other hand it is well known that organisms tend to vary in all 
5 Patten, W., Journal of Morphology, Boston, v. i, 1887, pp. 193-226. 
^Packard, A. S., Text Book of Entomology, 1898, p. 250. 
7 Leydig, F., Tafeln zur vergleichenden Anatomie, Tubingen, 1864, Figs. 
3 - 4 - 
8 Rabl-Rueckhard, Archiv. f. Anat., Physiol., und Wiss-Medicin, 1875, pp. 
480-499, pi. XIV. 
9 Carriere, J., Die Sehorgane der Thiere, Muenchen und Leipzig, 1885. 
10 Viallanes, H., Ann. Sci. Nat. Zool. 1887, 7 Ser. II, pp. 5-100, 6 plates. 
“Janet, Chas., Anatomie de la Tete du Lasius niger , Limoges, 1905, 40 
pages, 5 plates. 
“Burgess, E., 2nd Report, U. S. Ent. Comm., 1880, pp. 223-242, pi. IX. 
