52 AMERICAN FISHERIES SOCIETY. 



(jr, as it is often called, the Norway rat, as a species, became 

 more and more cosmopolitan. At the beginning- of the last cen- 

 tury this rat, a native of India, made its appearance in Europe, 

 having stolen a passage on the ships engaged in the India trade. 



It first appeared in England in 1730, and twenty years later it 

 had reached France. In Europe it drove out the black rat which 

 appeared in that continent during the middle ages ; the black 

 rat coming from no one knew where, having previously driven 

 out the native mouse which was the only representative of the 

 family known to the ancients. At the present time the brown 

 rat is everywhere, pretty much ; on the main lands of the globe 

 and the islands of all seas, wherever commerce sends its ships. 

 So too with the cockroaches [Blatta orientah's), a very cosmo- 

 politan and very disagreeable form of insect life. These two 

 familiar species are exceedingly active animals, and make their 

 way on board of vessels or hide in packages or merchandise, and 

 are thus carried on ships or cars, their inconspicuous size enab- 

 ling them to steal a passage. 



Again we have other illustrations of unintentional distribution 

 by man, where the trees, plants or seeds of one region are sent 

 to another. Upon the trees and plants thus transported often 

 occur forms like the scale bark lice, Aspidiotus and Lecanium ; also 

 the eggs of various insects. Many seeds contain the grub, 

 maggot or larvae of insect forms. If the roots of the trees or 

 plants are protected by a ball of the earth in which they grew, 

 and the earth if protected, by a cover of bagging, from crumb- 

 ling away and separating from the roots, a precaution which is 

 usually practiced by careful nurserymen, both earth and bagging 

 aflford a hiding place for small animals, such as insects (and 

 larvae of insects), worms, slugs and other small forms. If traffic, 

 through the facilities of its machinery, assists in distributing 

 plans that are useful to man, by the same system it contributes 

 to his discomfort and pecuniary loss. It is highly probable 

 that the scale bark lice, Aspidiotus aurantia (red scale) and Lecan- 

 ium olece (black scale), now such great pests to the orange growers • 

 of California, found their way into the citrus orchards of that 

 State, directly or indirectly, from the Australian acacias or, some 

 similar species of exotic trees, imported or planted for use or 



