respiratory organs, being- covered internally with very 

 thin cuticle. 



The circulation of the appendages is as follows : — 



(1) In the first antenna, the afferent vessel (PI. III., 

 fig. 1, a/f. v.^), which is a branch of the anterior aorta, 

 passes along the lower edge. On reaching the end of the 

 second segment most of the blood turns back along the 

 upper edge, but a little passes down a median vessel of the 

 fiagellum, returning bv the same channel, which is thus 

 alternately att'erent and efferent. The efferent vessel of 

 the appendage passes backwards just below the integu- 

 ment and opens into the anterior end of the pericardial 

 cavity. 



(2) In the second antenna, the afferent vessel, which 

 is also a branch of the anterior aorta, passes along the 

 iipper edge. The blood returns along the lower edge, the 

 efferent vessel passing backwards, more superficially than 

 the aorta, and emptying itself into the sternal sinus. 



(3) The mouth apjjendages are fed by two pairs of 

 branches given off by the anterior aorta, just behind the 

 (esophagus. Their efferent vessels apparently open into 

 the sternal sinus. 



(4) In the first four thoracic appendages the afferent 

 vessel from the sternal sinus passes down the posterior 

 edge to the tip, where it is continuous with the efferent 

 vessel, which passes up the anterior edge of the appendage, 

 and round the side of the body, opening into the dorsal 

 part of the pericardial cavit5\ As the afferent vessel 

 enters the proximal joint of the leg, it gives off a branch 

 (PI. lY., fig. 1, aff. hr. v.) to the branchia. This is a 

 highly vascular, thin, oval 2)late attached to the under side 

 of the leg and covered by very thin cuticle (PI. IV., fig. 3). 

 It has a striated appearance, due to the fine horizontal 

 bars of tissue, broken at intervals, which separate the 



