TRANSACTIONS OF THE SECTIONS. 139 
symmetry is the leading peculiarity of Pelonaia. It is this symmetry 
which renders the genus valuable to the comparative anatomist, as it 
reveals to him the relations of the different organs in the unsymmetrical 
Ascidians, and enables him to refer each of the former to its proper 
position in the series of organs in the animal kingdom. He is now 
enabled to state, with certainty, that the branchial vein, heart, and 
systemic artery of the typical Ascidians correspond to the dorsal 
vascular system of the annulose animals, and the systemic veins and 
branchial artery to the ventral vascular system in some of the latter. 
The annulated respiratory sac, and its lateral longitudinal attachment 
to the parietes of the body and to the symmetrical reproductive 
organs, the ventral position of the nervous centre, and excretory 
opening, all point to the same conclusion. The genus is equally 
valuable to the systematic naturalist, as it indicates the relations of the 
Mollusks to the annulose animals on the one hand, and to the Echino- 
dermata on the other. 
On the Regeneration of Lost Organs discharging the Functions of the 
fead and Viscera, by the Holothuria and Amphitrite, two Marine 
Animals. By Sir Joun G. DALYELL. 
The adult Holothuria resembles a cucumber, or a sausage, from six 
to twelve inches long, purple, yellow, gray or white. Some thousand 
suckers cover it like a shaggy coat, or disposed in rows according to 
species, affixing it firmly to solid substances, where it remains quiescent 
in a crescent form during the day; but when evening comes, a tuft, 
protruding from the larger extremity of the crescent, unfolds into 
a eapacious funnel, composed of eight, or ten, or twenty beautiful 
branches, implanted on a shelly cylinder, in the centre of which is the 
mouth. Each branch now begins to sweep the water in succession, 
and descends almost to the root within the mouth, in a contracted 
state, whence it arises to enlarge anew. These evolutions are pro- 
tracted until the latest hour; but as morning dawns, the whole 
apparatus is withdrawn, the skin close and compact as before, and a 
fountain begins to play from the opposite extremity. This singular 
animal is liable to lose all the preceding organic apparatus, consisting 
in the Holothuria fusus of eight longer and two smaller branches 
(tentacula), together with the cylinder, mouth, cesophagus, lower 
intestinal parts, and the ovarium separating from within, and leaving the 
body almost an empty sac behind; yet it does not perish. In three or 
four months all the lost parts are regenerated, and a new funnel, com- 
posed of new branches, as long as the whole body of the animal, begins 
to exhibit the same peculiarities as the old one, though longer time be 
_ required to attain perfection. Other species of the Holothuria divide 
spontaneously through the middle, in two or more parts, all becoming 
perfect ultimately, by the development of new organs. Yet the 
anatomical structure of the whole genus is so complex as to defy the 
skill of anatomists in discovering the proper functions of some of the 
