H. M. PARSHLEY 
11 
north. If we deny that such a species could have maintained 
its existence here throujih the period of glaciation, we must im- 
agine it repeatedly driven southward and later returning un- 
changed by its travels, which, being in a north and south direc- 
tion, would certainly prove far more eventful than the preceding 
journey from west to east. On the other hand, it could V)e argued 
that the uniform character of the immediate environment, under 
the dead l)ark of trees in certain pretty definite stages of decay, 
might well i)rotect the species from any evolutionary intluences 
which its wanderings might otherwise exert; but we must not 
overlook in this connection that the genus, compact as it is, con- 
tains more than a hundred distinct species, almost all of them 
produced under these apparently uniform conditions, and hence, 
while we must sujipose that these numerous forms have Ijecome 
differentiated through mutation, it is difficult to believe that the 
retreat and return could have been accomplished even once 
without setting in motion the forces underlying germinal change, 
which quite evidently have been particularly active in this genus. 
A few other species deserve especial mention in connection 
with the subject of geographical distribution. Aradus fnlleni is 
one of the few animals which are truly Xeogaeic; it occurs widely 
over South America, in ('entral America, and in North America 
as far northward as Connecticut and A'ancouver Island. Not- 
withstanding the vast extent of this range there is little varia- 
tion among individuals and never the slightest doul)t in deter- 
mination. By way of contrast in the matter of variation, we 
find that proboscideus, while fairly constant in specific characters, 
exhibits a considerable diversity in color and in structural details, 
more in keeping with its wide distribution — California, the Rocky 
Mountain region, and east across Canada to New Rngland. 
Abbas, although it occurs throughout the Nearctic region, pre- 
sents no variation worth mentioning, even in the narrow white 
annulation of the antennae, l)ut in lugubris a similar ornamenta- 
tion may l)e developed in varying degrees, cpiite independently 
of locality. It may be noted in passing that we have here an 
excellent illustration of the principle that characters pheno- 
typically identical may depend upon cpiite diverse' intc'rnal factors. 
The annulation of the antennae in a})bas is evidently the exprc's- 
sion of some constant element in the hereditary constitution 
of the species, while in lugubris these markings ai'e subject to 
individual somatic variation, with the possibility that Mendc'lian 
processes are also involved. 
TKAXS. AM. EXT. SOC., XLVII. 
