477 
ful influence on its evolution. If that is the case of Epizoie insects, we 
are not far wrong in assuming that the similarities, often slight in them- 
selves, which sympatric insects (i. e., insects living in the same district) 
exhibit, are due in the first instance to similarity in the surrounding pri- 
mary conditions of life.’’ * 
Among the Hymenoptera we have some most extraordinary 
examples of homoplasmy in wasps which inhabit figs. The true 
fig-wasps, or Agaonides, are wonderfully constructed for the life 
they lead, especially the male, which never leaves the fig, and 
passes its life among the forest of fig flowers; it is wingless, 
or nearly so, flattened horizontally, in many cases the middle 
legs are reduced or rudimentary, and the mandibles are large 
for gnawing open the galls containing the females; in fact, their 
whole morphology has been modified to adapt the insect to its 
activities within the fig. Other fig-inhabiting wasps belonging 
to quite different groups of genera, not taking any part in the 
polinization of the flowers, have males modified along similar 
lines. A thorough study of. the fig-inhabiting wasps, their rela- 
tionship and homoplasmy, would well repay a number of years’ 
close study. If any of the figs bearing open fruit have gall 
wasps attached to them, their study should be included, as they 
should throw light upon the origin of the relationship of insect 
to fruit. 
Wheeler, discussing certain ants, remarks: 
““We have here some very interesting cases of convergence, or parallel 
development, since the underground habit has caused the workers, which 
rarely or never leave their burrows, to lose their deep pigmentation and 
become yellow or light brown and to become nearly or quite blind.’’ 
Among the Arthropods we find many that breathe by tra- 
cheae, i. e., Prototracheata, Myriapoda, Insecta, Arachnida, and 
perhaps even Isopoda. If the tubes in Isopoda are really tra- 
cheae, then these organs had at least two distinct origins, and 
even leaving these out of account it is highly probable that 
among the four other groups tracheae arose at least twice inde- 
pendently. Gills have arisen quite independently in many groups, 
and several times in a single class, such as insects, and even 
more than once in the same order. 

* Pro. Ent. Soe. Lond. for 1916. September, 1917, exli, clvi, and figs. 
