XXXVv1 INTRODUCTION. 
branchial appendages and other parts of the system that 
from their transparency and tenuity may be conveniently 
examined, afford presumptive evidence against the circula- 
tion of the blood being confined to walled channels. 
In the Jsopoda, the branchial organs are variously diffe- 
rentiated. In some, as Ligia, for example, the passage of 
the circulating fluid through the branchial plates is clearly 
and distinctly defined (Fig. 12). The main artery, com- 
mencing at the base, gives off numerous lateral branches, 
that divide and sub-divide into a rich plexus with abundant 
capillary vessels. In the genus Sphkeroma, the branchial 
organs consist of a series of plates attached 
to the posterior wall of the fourth and 
fifth pairs of pleopoda (Fig. 13). In the 
degraded family of the Bopyride, the bran- 
chial organs are depauperated to the lowest 
degree, being in some genera little more 

than excrescences on the ventro-lateral 
margins of the pleon. 
In Tanais, the true branchiz have not been clearly 
determined. It is the opinion of Dr. Fritz Miller, Van 
Beneden, and Doctor Anton 
Dohrn, that an appendage 
attached to the first pair of 
gnathopoda is not a branchial 
organ, but a flabelliform ap- 
pendage, that by its constant 

Fie. 14, 
and unvarying motion induces the surrounding medium 
to flow over the branchial appendages that as yet have not 
been discerned. 
At page 122 of the second volume of this work we 
have described and figured one of the pereiopoda with a 
sac-like appendage attached, that we considered as the 
homologue of the branchial sae in the normal Amphipoda. 
