LTMNOLOGICAL PROBLEMS 
421 
within the higher many-celled organisms is but small, the reason lies 
far more in the great difficulty of these researches than that such cases 
are rare. Examples are known, however, of insects which, transferred 
from Europe to America, completely change their habits ; viz. the 
bean beetle in Europe (Haltica imfipes)^ which in America attacks 
fruit-trees ; Anthrenus scropliular'ise^ which in Europe feeds on blossom- 
ing fruit-trees, but in America lives in houses and causes great 
damage to carpets and furniture. Further species occur, e.g.^ among 
gall-flies, morphologically not to be distinguished, but biologically 
very different, and producing galls of great diversity in appearance 
{Cynips capiit-medm^, C. calicis). Also, the attacks of the Kea upon 
the New Zealand sheep may be mentioned. 
From these biologically separated groups of individuals the 
morphological form series may arise, the specific biological functions 
produced by external circumstances causing variation in outer shape. 
The reason why such cases are so rare is the great difficulty of 
following the development or of finding any fixed stages in the chains 
of forms which might show the development. As examples may be 
noted the biological division of species of parasitic insects with regard 
to the different animals on M^hich they live and their consequent 
variation in colour (Sajd, 1904, p. 372) ; the nut-cracker {Caryo- 
catactes nucifraga)^ which in Siberia lives on the seeds in the cones of 
the Siberian cedars, in Europe mainly on nuts, acorns, etc. ; in Siberia 
its beak is longer and narrower, in Europe stronger (Weismann, 1902, 
p. 378) ; here we possibly have to deal with a horizontal series of 
forms derived from a morphological series, which again has had its 
starting-point in biologically separated groups. 
It hardly requires to be pointed out that the single links in a chain 
of forms are naturally not arranged either horizontally (through space) 
or vertically (through time) with such great regularity that the forms 
with the best buoyancy apparatus are invariably found farther south 
or in higher earth-strata than those with less developed apparatus. 
During the melting period of the ice there have been times when the 
temperature fell after rising ; and in many tracts of land where the 
climatic conditions might ordinarily be considered as tempera^te, 
localities occur with temperatures many degrees lower than the normal 
for the latitude of those parts. Far to the north, on the other hand, 
there are places, for example on the southern faces of mountains, where 
the temperatures are much higher than the normal for the region 
(G. Andersson, 1902, p. 1 ; 1906, p. 45). At such periods and localities 
there will naturally be some irregularities in the chain of forms. At 
times and places, possibly with higher temperatures, forms will appear 
with a greater development of the apparatus for floating than those in 
recent geological strata and farther south, just as the reverse may 
