20 MEMOIR II. 



of tlie valvular pouch of the other sex ; they have further 

 the addition of an appendage at the bifurcation of the 

 inner antennse, so densely tufted as to resemble a brush, 

 (Plate I. fig. 5;) it is probably this appendage which has 

 induced Naturalists erroneously to assign to Mysis, trijid 

 interior antennae. 



Hitherto, the Opossum Shrimps have not been observed 

 further South than the precincts of the English Channel, 

 but they occur as far to the North as the icy seas of the 

 Polar regions, where they must exist in very great abun- 

 dance during the summer season, as they are said by 

 O. Fabricius to constitute one of the principal sources of 

 nutriment to the Whale, Avhich taking in myi'iads at a gulp, 

 separates them from the water by means of its complicated 

 strainers, and swallows the congregated pabulum which 

 they now form, at leisure ; we should hardly give credence 

 to the fact, that an animal so disproportioned, should con- 

 stitute the food of this Leviathan, did we not perceive that 

 the peculiar structure of the mouth, and smallness of the 

 gullet in these enormous creatures (the MysticeteWhales) 

 is in perfect accordance, and fits them for separating 

 small and soft animals of every kind from the sea water, 

 while it precludes the power of masticating, or of swallow- 

 ing bodies of even moderate size : abundance in this 

 instance, makes up for the individual smallness of the 

 prey, and these little animals must be allowed to be a 

 much more substantial food than the medusae, upon which 

 the whales are also understood to feed. In these climates, 

 the Opossum Shrimps serve as food to the herring and 

 pilchard, and probably to many other fishes, and although 

 by their numbers they might tempt the epicure to serve 

 them up in the aggregate, as they do the young fry of 

 fish in some parts of the world, the species with which wc 

 arc best acquainted arc so little particular in their food as 

 to counteract any design wc might form upon them 5 this 

 objection however, does not apply to the oceanic spccics> 



