122 TANAIS. 



the body, also, to which they are attached, is shorter 

 than the remainder. They are simple in their structure, 

 and terminated by a long, slender finger. The five re- 

 maining pairs of legs are also simple, and gradually but 

 slightly thickened from the third to the seventh pair, 

 which is the thickest. The slender membranous plates 

 forming the incubatory pouch in the female are attached 

 to the base of several of the intermediate pairs of legs. 

 Fritz Miiller, in his remarkable work " Fur Darwin " 

 (8vo. Leipzig, 1864, p. 11), gives a lateral view of Tanais 

 dubius of Kroyer, with the second, third, fourth, and 

 fifth pairs of legs respectively furnished at the base 

 with a small oval plate, which he describes as the 

 " Anlagen der blatter die spater die Bruthohle bilden." 



LEG OF TANAIS. 



We here give a figure of the fifth leg of Tanais vittatus, 

 from the coast of Devonshire, having an appendage 

 at its base, which we regard as a branchial sac similar 

 to those existing in the Amphipoda, and consequently 

 affording a proof of the nearer relationship of Tanais 

 with that order than is possessed by any other isopodous 

 animal. This appendage is wanting in some specimens, 

 and its variable existence is probably a character of 

 specific distinction in the group. Moreover, as we have 

 found it in the largest-sized specimens, we apprehend 

 it cannot be regarded as the rudiment of the plates 

 that form the incubatory pouch, as Dr. F. Miiller con- 

 siders those of T. dubius to be. 



