242 
IOWA ACADEMY OF SCIENCES 
Minnesota, L. 10-oculatus and L. %-ociilatus, are interesting in their 
stages of ocellar atrophy. See figures 11 and 12. In the former the 
eyespot is shortened and C forced in from the margin as in Papirius, 
fig. 9. This ocellus is small, while the two preceding it are large. D 
has apparently disappeared, and from the position of the next ocellus, 
it seems probable that E has also atrophied. Two are found in the 
caudal end of the eyespot which are probably F and G, if we assume, 
as we safely may, the atrophy of H. In the closely allied L. Q-oculatus 
the small ocellus C has been lost, also one corresponding to the smaller 
of the two caudally placed ones in Fig. 11. This leaves for L. 6-octilatus 
only A, B and F, a considerable portion of the eyespot between the 
first two and the last being destitute of ocelli. This intermediate 
space, having lost the ocelli, has also lost its pigment; and there remain 
a cephalic and a caudal spot, containing, respectively, two and one 
ocelli. In the genus Isotoma' there is a species, Isotoma i-oculata Tull- 
berg. Fig. 13, with similarly, divided eyespots, but in this the cephalic 
portion contains but one ocellus. Probably, from its positional relation 
to the postantennal organ, it is ocellus B, and the caudal spot contains 
F. In Wahlgren’s species Isotoma hinoculata, the small cephalic spot 
alone is present, and contains the single ocellus. In the blind species 
Isotoma fimetaria (L), there is no evidence of ocelli or even of pig- 
mented areas. In the genus Sminthurus v/e have a blind species in 
which some specimens possess very little pigment upon the general 
surface, while others show a considerable amount of fine reddish pig- 
ment dots. This species does not possess ocelli, and seldom shows 
evidence of a pigmented eyespot, but some specimens have been taken in 
which unmistakable pigmented areas representing eyespots were present. 
A species very closely related, structually, but with a well-pigmented 
body, shov/s a single small ocellus on each side of the head situated on 
a very small black eyespot. This ocellus is probably either A or B. 
There are but a few examples of the peculiar conditions of ocellar 
atrophy obtaining among this interesting group, but they may be suf- 
ficient to call attention to the following conclusions: The number and 
arrangement of ocelli, subject to various modifications may be recognized 
throughout the Collembola. Members of this group occupying marginal 
positions have greater tenacity of existence than others. Central ocelli 
are usually the first to go. A more advanced stage of atrophy deprives 
the whole middle part of the eyespot of ocelli and at the same time or 
a little later of its pigment. The last part of the eyespot to persist with 
its ocelli is the most cephalic end. Vestigial pigment may determine 
the position of an eyespot after all the ocelli have been lost. 
