The experiments, that I made, were on the common English Barnacle, which is very frequently met with, at this time of the year, on oysters and other shell-fish. The microscope, that I made use of to observe it, was Mr. Cuff’s aquatic one; where the animal, when taken out of the shell, may be put into the watch-glass with salt water, or spread on the round glass plate on the stage of the microscope, and kept moist with a hair pencil and salt water during the time of observation: this will keep the claws and proboscis alive and in motion for many hours together. This animal has 24 claws, or cirrhi (_See Fig._ A), which are disposed in the following manner: the 12 longest stand erect, arising from the back part of the animal: they are all joined in pairs near the bottom, and inserted in one common base. These appear like so many yellow curled feathers: they are clear, horny, and articulated. Every joint is furnished with two rows of hairs on the concave side. The animal, in order to catch its prey, is continually extending and contracting these arched hairy claws, which serve it for a net. The 12 smallest claws are placed next to these, six on each side: these are divided into pairs; that is, two claws to one stem, like the chelæ or claws of the crab. These are more pliable, and fuller of hairs, than the others, and seem to do the office of hands for the animal. The whole number of claws lessen in size gradually each way, from the tallest in the back, to the last but one of each side in the front; which last two are of the middle size. The proboscis, or trunk, rises from the middle of the base of the larger claws, and is longer than any of them: this the animal moves about in any direction with great agility: it is of a tubular figure, transparent, composed of rings lessening gradually to the extremity, where it is surrounded with a circle of small bristles, which likewise are moveable at the will of the animal. These, with other small hairs on the trunk, disappear when it dies. Along the inside of this transparent proboscis the spiral dark-coloured tongue appears very plain: this the animal contracts and extends at pleasure. The mouth appears like that of a contracted purse, and is placed in front, between the fore claws. In the folds of this membraneous substance are six or eight horny laminæ or teeth standing erect, each having a tendon proper to direct its motion. Some of these teeth are serrated, others have tufts of sharp hairs instead of indentations on the convex side, that point down into the mouth; so that no animalcule that becomes their prey can escape back. Under the mouth lie the stomach, intestines, and the tendons by which they adhere to the shell. This then is the general character of the animal of the whole genus, whether with stems or without.