and having assimilated and digested this, they then eject the harder materials. The motion of the body in consequence of its contractions is much like that of leeches, and on this account these Synaptæ were long supposed to be a transition type between the Radiates and worms. The body grows to a great length, often half a yard and more, but constantly drops large portions from its posterior part, by means of its own contractions, or breaks itself up by the expulsion of the intestines, which are very readily cast out. The tentacles are hollow, consisting of a central rib with branches from either side. In the Synaptæ, as in all the Holothurians, the madreporic body is placed near the mouth, between two of the ambulacra, and opposite the fifth or odd one. The tube, connecting with the central tube around the mouth, by means of which it communicates with the ambulacral tubes, is very short. [Illustration: Fig. 125. Anchor of Synapta; _a_ anchor, _w_ plate upon which anchor is attached; greatly magnified.] _Caudina_. (_Caudina arenata_ STIMPS.) [Illustration: Fig. 126. Caudina arenata; natural size.] Several other Holothurians are frequently met with on our shores. Among them is the _Caudina arenata_ (Fig. 126), a small Holothurian, yellowish in color, and thick in texture, by no means so pretty as the white transparent Synapta; the tentacles are short, resembling a crown of cloves around the mouth. It lives in the sand, and may be found in great numbers on the sandy beaches after a storm. _Cuvieria_. (_Cuvieria squamata_ D. & K.) [Illustration: Fig. 127. Cuvieria; natural size.]