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 “ Fir Darwin ” 
(8vo. Leipzig, 1864, p. 11), gives a lateral view of Tunais 
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 Tunais 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 jis 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 7. dubius to be. 
