50 REPORT— 1855. 



assurance that we can arrive at the conclusion of their veritable purpose. But 

 from their general position and structure, their constant presence both in male 

 and female, old as well as young, together with the form of the entire appa- 

 ratus, we are induced to believe them to be a simple form of urinary orgnn. 

 The contents, under a one-fifth power of the microscope, are resolved into 

 small round cells, containing a nucleus of granular material (PL XIX. fig. 6). 

 These cells are closely packed together, but not so firmly as to lose their 

 original form ; and the whole are confined within the walls of the organ, 

 which appear to be very stout, the external surface of which is slightly 

 notched (fig. 5) at tolerably regular distances, as if the organ had the power 

 of contraction and expansion. Both the organs (if there are always two, of 

 •which we are not certain, in every species, since we have not clearly de- 

 monstrated them, except in Sulcafor) (fig. 2) lie so closely together, as to 

 appear like one ; but in the genus Sulcator we have displayed them both by 

 dissection. They lie their full length along about one-third of the upper 

 aspect of the alimentary canal, and towards the posterior extremity make a 

 sudden turn, and directly after connect themselves with the alimentary canal 

 (fig. 1). The appearance of the structure at this bend is of a much more 

 robust character than at any other point of the organ. 



The Vascular System. — At the anterior portion of the alimentary canal, 

 and placed above it, lies the cardiac vessel or heart (PI. XXII. fig. 3 a). It is 

 a long simple organ more like an aorta than a heart, reaching from the first 

 to the last segment of the pereion (or thorax), and does not extend, as 

 asserted in the ' Histoire des Crustaces' (vol. i. p. 98), " through the whole 

 length of the abdomen," as is the case, upon the same authority, in the Sto- 

 mapoda. The superior wall is suspended by a series of attachments at the 

 centre of each successive segment, which gives it a festooned appearance 

 through the whole length of its upper surface. The walls of the organ are 

 of a fibrous character, arranged diagonally to the vision under the micro- 

 scope, the result we believe of a spiral arrangement in the general structure 

 of the walls. The whole possesses an elastic nature, and a persistent pulsation 

 is carried on, causing the festoon on the upper surface to rise and fall with 

 each successive throb. 



Corresponding with the centre of each segment there is an aperture in 

 the heart into which passes the blood, being propelled by successive 

 jerks (PI. XXII. fig. 3 c, c, c). The (so-called) blood-corpuscles are very 

 discernible, and by this means the course of the circulation is not difficult 

 to be traced. Though the corpuscles travel in a continuous current, yet we 

 have never been able to distinguish that this channel is bounded by walls, 

 in fact that there are any true blood-vessels. That none exist we think may 

 be strongly inferred from the fact elucidated by close and continued obser- 

 vation of the circulation, where two currents, an arterial and a venous, 

 travel in close proximity to each other; an occasional corpuscle from the 

 arterial may be seen to pass over to the venous without traversing the 

 greater circuit followed by the others. 



An arterial current passes through the whole length of the animal imme- 

 diately above the alimentary canal, and the great venous course returns 

 along the dorsal centre; at the commencement of the pereion (thorax) the 

 current appears to descend, and becomes confused to observation with the 

 arterial channel. (Vide diagram, PI. XXII. fig. 3.) 



The legs are nourished by a single arterial current and its venous return ; 

 in the broad plates of the coxae the arterial course passes down through the 

 centre, where it diverges and returns as two venous currents, the one on the 

 anterior, the other on the posterior margin. Near this point are situated 



