AND DISTRIBUTION OF THE FIROLIDA. E VA 
what is the range of each. Certain of them, e. g. Carinaria mediterranea, found chiefly 
in the sea after which it is named, have a fixed and limited home, out of which they are 
prevented from straying into materially colder or warmer waters by surrounding land, 
except when accidentally borne into the Atlantic by the efferent Gibraltar current. But 
it is not so with the majority of this group, which have not an inland and almost land- 
locked sea like this in which to swim, but great oceans, whose waters are being con- 
stantly changed by those mighty currents that form so marked a feature in their physical 
geography; and it is a question of some interest how arctic, temperate, and tropical 
varieties comport themselves in other zones,—whether or not they are drifted about 
involuntarily and helplessly, and kept continually circling round the globe, subjected in 
the many and rapid changes of latitude to equally sudden and great Yaribeions in the 
temperature and specifie gravity of the fluid in which they float, and if, for example, 
tropical forms can exist in arctic seas, which are known not to have the same low tem- 
perature as the air overhead, or, on the other hand, arctic forms in tropical waters. To 
this our still restricted knowledge does not appear sufficient to warrant more than a 
limited and indefinite answer; but it is likely that, as with land and the largest forms 
of aquatic animals, each has its own special region where it is found in the greatest abund- 
VOL. XXVII. 20 
