STOMAPODA. - MYSIS, OR OPOSSUM-SHRIMP. 255 



preceding, we may first notice the curious genus Mysis^ or 



Opossum-Shrimp ; which bears, in its general form, so strong a 



resemblance to the ordinary Shrimps, that it has been usually 



placed with them. It is distinguished, however, from the true 



Decapoda, by the external position of its branchiae ; as well as 



by other characters. In regard to the number of the feet, it 



holds a very interesting intermediate 



place between the Decapods and the 



ordinary Stomapods ; for the last 



pair of feet-jaws is developed into 



true legs, making their number 



twelve in all; and the other two 



pairs have much more the form of 



ordinary legs, than in the Decapods. 



Each of the legs has a lateral ap- FIG 479 ._ MYSIS VuLOARIS> about 



, which is SO much developed twice the natural length : a, one 



,., , ,. , , of the bifid legs. 



as to appear like a second limb ; and 



thus, reckoning-in the feet-jaws, which also possess similar 

 appendages, we may say that the Mysis has no fewer than 32 

 legs. The common name of this curious little animal is derived 

 from the peculiar conformation, which enables it to afford a 

 special protection to the eggs. The female has a large concave 

 scale, attached to the inner division of each of the posterior legs ; 

 and these, overlapping one another, form a pouch, which is 

 capable of being considerably distended. Into this pouch the 

 eggs are received, when they quit the ovarium ; and here they 

 continue until the young are so nearly developed, that they pre- 

 sent a very close resemblance to the parent. The parent then 

 opens the valves of the pouch, and sets free the whole brood at 

 once into the surrounding element; and these usually seem 

 to remain associated with the community, from which they 

 sprang. Although sparingly distributed in the seas of Europe, 

 these little animals inhabit some parts of the Arctic ocean in 

 amazing numbers; constituting the principal food of the pro- 

 digious shoals of Salmon, which resort thither in the months of 

 July and August, and upon which the inhabitants of Boothia 

 depend in great degree for their winter store of provisions ; and 



