Miscellaneous. 85 



as the he:irt, to which the vertical canal is intimately united, but 

 without havinj^ any relations to it except those of contiguity. The 

 organ in (jue.stion is therefore not a heart, as has hitherto been believed ; 

 and we shall recur immediately to its structure. Having arrivid at 

 thepoint where the oesophajius penetrates into the lantern, thevertical 

 A'essel opens into a circular vessel resting on the superior membra- 

 nous floor of the lantern and bearing opposite to each of the i)yramid3 

 a small racemifoim gland (Poll's glands). This, whatever may have 

 been said, is the only vascular ring presented by the circulatory ap- 

 paratus of the Echinida ; at least I have found it impossible to discover 

 any other. From this ring, opposite to the intervals of the pyramids 

 and consequently alternating wuth Poll's glands, spring five radiating 

 vessels which ])ass beneath the calcareous piece known as the f(tf>r, 

 and become widened so as to occupy the whole width of the inferior 

 surface of this piece. Arriving at the outer margin of the lantern 

 these radiating canals resume their original calibre and run along 

 the outer surface of the lantern, from which, however, they finally 

 separate, so that each of them may become continuous with one of 

 the five ambulacral canals. The latter are produced a little towards 

 the mouth beyond their point of junction with the five vertical canals; 

 it is this, no doubt, that has led to the belief in the existence of a vas- 

 cularring applied to the buccal membrane within the lantern; but this 

 ring has no existence : the prolongations of the ambulacral canals 

 soon bifurcate ; and each of their branches penetrates into one of the 

 two large buccal tentacles. 



The ambulacral canals ascend along the test, and terminate ccecalhf 

 below the pore presented by the so-called ocular plates, although 

 these do not contain any organ of vision. In Echinus sphcera this 

 pore is closed by a continuous membrane, and does not give passage 

 to any thing resembling an unpaired tentacle. Although one can 

 inject the whole circulatory apparatus by applying to one of these 

 pores the pipe of a syringe, there is not in it any direct communi- 

 cation between the vascular apparatus and the exterior ; the injec- 

 tion only penetrates in consequence of a lesion. There is no anal 

 ring uniting the five ambulacral vessels. Each canal is the seat of 

 a double current maintained by the vibratile cilia which clothe its 

 interior ; it serves at once for the flow and the return of the san- 

 guine liquid which it contains, as I have been able to ascertain by 

 direct observation. The arrangement of the ambulacral vessels of 

 the Echinida therefore exactly reproduces that which I have already 

 described in the Comatulce. 



Immediately opposite to the right upper Poll's gland there springs 

 from the circular vessel of the lantern a vascular branch which 

 ascends along the oesophagus, and forms, to a certain extent, a pen- 

 dant to the vertical canal which originates from the madre])oric 

 plate and opens at the left posterior Poll's gland. Having reached 

 the point where the oesophagus opens into the intestine, this canal 

 becomes reflexed and considerably widened, and constitutes the great 

 vessel which follows the inner margin of the intestine, and beyond 

 which the mesenteric plate is slightly prolonged. There is con- 



