LESSON 45.] NUTRITION IN THE BKACHIOPODA. 



157 



like the intestine, and for the same purpose to compel FrG - 254 - 

 the mature ova to pass through the aperture of the 

 vent, when open. 



696. In the beautiful and luminous Pyrosoma (Fig. 

 254) we have an interesting example of a compound 

 molluscan group. The external tunics of the individu- 

 als composing this group, are thin, soft, very trans- 

 parent, and of a bluish white color, and are the parts 

 by which they appear to be united together. 



697. The Pyrosoma is a long tube shaped like a 

 finger, closed at the upper end (a), and open at the 

 lower extremity (6), and composed of a great number 

 of distinct individuals (c), which possess an internal 

 organization similar to the Cynthia. Like the latter, they also pos- 

 sess two orifices, but their position is different ; their respiratory 

 apertures are placed on the sides of the long projecting papillae (c), 

 and the apertures constituting the vents of all the separate individu- 

 als, open into the interior of the tube ; so that, solely by the com- 

 bined act of respiration, this elegant tube is carried through the seas. 



The species of this animal common to the Atlantic (Pyrosoma 

 gigantium), is of about the length of two fingers, and when seen on 

 a still night, or, better still, if captured and conveyed in a basin of 

 sea- water into a cabin, is an object of remarkable beauty. 



Pyrosoma gi- 

 gantium. 



LESSON XLY. 



NUTEITION IN THE BEACHIOPODA. 



698. There are only three orders of this class, the Lingula^ Orbi- 

 cula, and Terebratula. These are all protected by shells, and attach 

 themselves to foreign substances, the Lingula (so called because 

 tongue-shaped) by means of a very long peduncle (Fig. 255 A), which 

 passes between the two valves : a, the shell, 5, the peduncle ; and 

 the Terebratula, by a much shorter peduncle, which projects through 

 a hole in a beak-shaped prolongation of one of the valves. 



699. In the latter the alimentary tube is very short, of great 

 simplicity, and confined to a small space. The rest of the interior 

 of the lobes of the mantle is occupied by three long, strongly ciliated 

 arms, disposed in folds and spiral curves. The bases of the arms 



