294 MANUAL OF ZOOLOGY. 



oral processes, which are termed the " arms," and from which 

 the name of the class has been derived (fig. 105, i)j These 

 organs are lateral prolongations of the margins of the mouth, 

 usually of great length, closely coiled up, and fringed -on one 

 side with lateral processes, or " cirri." In many Brachiopods 

 the arms are supported upon a more or less complicated inter- 

 nal calcareous framework or skeleton, which is sometimes called 

 the " carriage- spring apparatus." 



Fig. 105. — "BrsxAiio^ioAsi {Terebratula vitren). t. Showing tlie ciliated "arms;** 

 2. Showing the shell with its loop, (After Woodward.) 



The mouth conducts by an oesophagus into a distinct 

 stomach, surrounded by a well-developed granular liver. The 

 intestine has a " a neural flexure," and " either ends blindly in 

 the middle line, or else terminates in a distinct anus between 

 the pallial lobes."- — (Huxley.) 



Within the pallial lobes there is a remarkable system of 

 more or less branched tubes, anastomosing with one another, 

 and ending in csecal extremities. This, which has been termed 

 by Huxley the " atrial system," communicates with the peri- 

 visceral cavity by means of two or four organs which are called 

 " pseudo-hearts," and which were at one time supposed to be 

 true hearts. " Each pseudo-heart is divided inio a narrow, 

 elongated, external portion (the so-called ' ventricle'), which 

 communicates, as Dr Hancock has proved, by a small apical 

 aperture, with the pallial cavity ; and a broad, funnel-shaped, 

 inner division (the so-called ' auricle') communicating, on the 

 one hand, by a constricted neck, with the so-called ' ventricle;' 

 and, on the other, by a wide, patent mouth, with a chamber 

 which occupies most of the cavity of the body proper, and 

 sends more or less branched diverticula into the pallial lobes." 

 — (Kuxley.) This system of the atrial canals has been looked 

 upon as a rudimentary respiratory apparatus ; but its function 

 is more probably to act as an excretory organ, and also to 

 convey away the reproductive elements, the organs for which 

 are developed in various parts of its walls. By Woodward 



