186 THE ORGANIZATION OF STARFISHES 



In addition to this there is another system (/>, 6 1 , & 2 , 6 3 , b*, b 5 ) 

 of tubes which embraces the outskirts of the stomach, and sends 

 off a minute branch (b 5 ) to each of its ten puckered, chylific sacs 

 (st 1 ). It has been asserted by some observers that this system 

 is connected with the other one by a vessel which runs along the 

 madreporic canal (m 1 ) and forward to the canal (aq) about the 

 throat ; but of this there is a divided opinion among anatomists, 

 some insisting that no such relation exists. This is all owing 

 to the minuteness and delicacy of these tubes, and the consequent 

 great difficulty of investigating their relations. It has, however, 

 been rendered more probable that they are distinct systems, the 

 one emanating from the region of the mouth being devoted to 

 the circulation of a watery fluid, and the other forming, more 

 probably, a blood circulation. 



Last in the list of these manifold repetitions, the reproductive 

 organs come under our notice. These are ten in number, in 

 five pairs (r, r 1 , r 2 ). They stretch along the sides of the arms, 

 two in each, for a short distance, and, branching on one side, send 

 off their minute twigs into the general cavity. They arise near 

 the angles of the arms ; and it is at these points (r 1 ) that each 

 discharges its eggs in the breeding season. From here they 

 gradually taper to the opposite extremity, (r 2 ,) and terminate 

 merely as irregularly shaped tubules, of an apparently very sim- 

 ple organization. 



We have, then, no less than five, or perhaps six, different sets 

 of organs arranged along the sides of this foreshortened, quin- 

 tuplicate tube, among which some of them exhibit a fivefold, and 

 others a tenfold repetition. How, and by what consecutive grada- 

 tions these parts are reduced in numbers as we rise in the scale 

 of successively higher forms, until we meet with the most emi- 

 nent, singularly worm-like Trepangs, I have not sufficient space 

 here to enlarge upon ; but I must not fail to point to one remark- 

 able fact which keeps itself most prominent during, and as an 

 accompaniment to, these changes, namely, that the reduction 



centricity of the madreporic plate in certain Echini would be cited as an objec- 

 tion here by no one but such as would mistake bisyinmetry for bilaterality. 



