GAMMARUS. 351 



transverse vessels (PI. IV., fig. 3, tr. br. v.). A large vessel 

 (PI. IV., fig. 3, aff. br. v.) runs round the edge of the 

 branchia, the two sides of the loop being connected by fine 

 transverse vessels, occasionally anastomosing, in which 

 the blood is brought into the closest contact with the 

 water. The blood passes down the posterior edge, some 

 of it flowing through the transverse vessels, some flowing 

 right round the branchia, not leaving the large encircling 

 vessel, which returns up the anterior edge and empties 

 itself (PI. IV., fig. 3, eff. br. v.) into the efferent vessel of 

 the leg (cp. PI. III., fig. 1). A separate afferent vessel 

 from the sternal sinus enters the middle of the coxal plate 

 (PI. IV., fig. 1, cp., and PI. III., fig. 1), which is very 

 large, especially in the fourth thoracic segment. Passing 

 down to the lower edge of the plate, it bifurcates, each 

 branch following more or less closely the edge of the 

 plate. These efferent branches (PI. III., fig. 1, eff. c. v.) 

 reunite at the top of the plate and empty themselves into 

 the efferent vessel of the appendage. In the female, 

 another branch from the afferent vessel of the leg supplies 

 the oostegite, the efferent vessel from which empties itself 

 into the efferent vessel of the appendage. 



(5) The last three thoracic legs have no enlarged 

 coxal plates or oostegites, but they bear branchise. The 

 afferent vessel passes down the anterior edge of the leg, 

 giving off a branch to the branchia as in the first four 

 thoracic legs ; the efferent vessel follows the posterior edge 

 and receives the efferent branchial vessel as it leaves the 

 leg (PI. IV., fig. 1). 



(6) In the abdominal appendages, which do not bear 

 branchia?, the blood passes down the anterior margin and 

 up the posterior one, as in the last three thoracic legs. 

 The first three abdominal appendages — the meropods — are 

 protected by large epimeral plates (PL III., fig. 1, epim. 



