Testacea

Peculiar among the Testacea are the sea-urchins and the animals known as Tethya (Ascidians).

On the Parts of Animals 2002

Purpuras and Whelks, and all other Testacea that have turbinate shells, in structure resemble the Sea-snail.

On the Parts of Animals 2002

The former is incorrectly termed ovum, for it merely corresponds to what in well-fed sanguineous animals is fat; and thus it is that it makes its appearance in Testacea at those seasons of the year when they are in good condition, namely, spring and autumn.

On the Parts of Animals 2002

This is plainly to be seen in flies and bees and all such animals, and likewise in some of the Testacea.

On the Parts of Animals 2002

It should, however, always be looked for in some midway position; namely, in such Testacea as are stationary, midway between the part by which food is taken in and the channel through which either the excrement or the spermatic fluid is voided, and, in those species which are capable of locomotion, invariably midway between the right and left sides.

On the Parts of Animals 2002

For the Testacea, while in some points they resemble the

On the Parts of Animals 2002

For it would be in opposition to what prevails in the whole tribe of Testacea; for in all the ovum is discontinuous, and in all excepting the sea-urchins asymmetrical, being placed only on one side of the body.

On the Parts of Animals 2002

For here the two extremities are brought together by a curve, as if one were to bend the straight line marked E until D came close to Such, then, is the disposition of the internal parts; and round these, in the Cephalopoda, is placed the sac (in the Poulps alone called a head), and, in the Testacea, the turbinate shell which corresponds to the sac.

On the Parts of Animals 2002

But the Cephalopoda and the turbinated Testacea have in common an arrangement which stands in contrast with this.

On the Parts of Animals 2002

All the Testacea then, those that have not been mentioned as well as those that have, agree as stated in possessing a mouth with the tongue-like body, a stomach, and a vent for excrement, but they differ from each other in the positions and proportions of these parts.

On the Parts of Animals 2002