The author observes generally, respecting the Vermes of Linnæus, that the blood is conveyed by veins to the respiratory organs, and from thence by arteries to the heart, in which they differ from fishes; while they differ, on the other hand, from Mollusca in general, by having red blood.
The Sepia has been thought to have a circulation peculiar to itself; but the author remarks, that it bears a close resemblance to that of the Teredo, in having two auricles which transmit the blood received from the bronchiæ to the heart, but differs in this, that there are also two auricles that receive the venous blood, and transmit it to the respiratory organs.
The animal here described under the name of Hirudo vulgaris, is the same that has been denominated by Linnæus and others, Hirudo octoculata, on account of the number of its eyes; but since the Hirudo tessulata has also eight eyes, it has been thought proper to change that name for one not liable to mislead.
This little animal is found very commonly in rivulets, attached to the under surface of stones. Its length varies from one inch to an inch and an half. The back is of a dark brown, marked with numerous transverse lines, and a central line longitudinally of a black colour. On the belly also is a longitudinal black line, but the rest is of a yellowish-green colour.
In structure this animal very much resembles the Hirudo medicinalis, having the anus at the extremity of the tail, and four longitudinal vessels destined to convey the circulating blood, one dorsal, one abdominal, and two lateral. In these, eight pulsations are observable in the course of a minute, but not derived from any central organ corresponding to the heart of other animals.
Its food consists of very small worms, which it swallows whole.
The object of the present communication is to record such peculiarities as the author has observed in its mode of propagation, to which he has paid attention during the last two summers.
Having found a pair of them copulating as hermaphrodites, like the common snail, on the 13th of August, he watched the period at which eggs were deposited, and found a capsule of eggs produced on the 17th, and another on the 18th, both of which were subsequently hatched. The same leech also laid as many as seven more capsules, at intervals of two or three days in succession, but all these last seven proved abortive.
Those which were productive showed signs of life in three weeks, and in five more the young made their escape from the capsule.
The capsule in which the eggs are deposited is formed as a membranous ring, surrounding the body of the parent in the region of
