VARIETIES. 
59 
owing to the deferred development of .some of the organs of the 
animal, or other causes, as in those specimens where banding or other 
ornamentation, though not present in the early or youthful stages, 
become gradually developed and intensified as growth proceeds ; or 
the change from the parental characters may be the apparently direct 
result of external causes, as has been demonstrated by Herr Hazay, 
who has developed the short-spired globose form of Liiunwa peregnt 
from the ova of the elongated typical form of the species, and vlce- 
cersd, according as the ova were placed and reared in still pools, or 
in “hard” running waters. 
If the circumstances favouring certain variations be practically of 
a permanent character, and affect the bulk of the individuals of a 
species throughout a whole district, as may be the case where the 
apparent determining causes are physical or climatic, or as they have 
been termed Ectergogenetic, the modified form becomes hereditary 
and is then termed a sub-species, geographical variety, or race. 
These geographical varieties often have many of the characteristics 
of good species, possibly as a conse(iuence of long isolation from the 
typical form, and they cannot always with certainty be specifically 
determined, even after an e.xamination of the structure of the animal; 
thus according to Simroth the species of the genus Amalia are very 
unstable, eacli country impressing its own local stamp upon the 
species inhabiting it, and the majority of forms set up as distinct 
species by viirious authors are only transition forms bridging o'ver 
the interval between carinata and sowerbyi on the one hand and 
carinata, and gagates on the other. Some species and genera are 
however less subject to variation than others, and the.se groups or 
species showing least adaptability to modified circumstances are 
usually more or less restricted in their distribution. 
The term Varieties when used in a restricted sense, refers to in- 
dividuals which have developed or acquired very noticeable differ- 
ences from the typical or parent form, but have not occupied any 
special district to the virtual exclusion of the type, but coexist with 
it, being more .sporadic and isolated in their occurrence, possibly 
owing to the prediisposing causes being of a limited or evanescent 
nature, or perhaps intrinsic to the individual, and not therefore of so 
general and pervading a character as is the case where the mass of 
the individuals inhabiting .some definite area are affected, as in the 
geographical varieties. 
