, 
192 INVERTEBRATE ANIMALS. 
podes, feet). The arms also serve as respiratory organs, and 
in many forms they ate supported on an internal calcareous 
framework or skeleton, sometimes called the *‘ carriage-spring 
apparatus.” 
The mouth is placed between the bases of the arms, and is 
not furnished with any apparatus of teeth. It conducts bya 
gullet into a distinct stomach, surrounded by a well-developed 
granular liver. The intestine may or may not be furnished with 
a distinct anus, but in no case does it open into the body-cavity. 
Within the lobes of the mantle there is a remarkable system of 
branched tubes, which commence by blind extremities, and 
finally communicate with the mantle-cavity by means of cer- 
tain organs which were formerly believed to be hearts, and are 
now known as “pseudo-hearts.” This system of tubes appears 
to be mainly, if not entirely, connected with reproduction. A 
true heart, however, is present in most, if not in all, of the 
Brachiopoda. 
The nervous system consists of a single principal ganglion, 
connected in some cases with others so as to forma collar 
round the commencement of the gullet. In some cases, how- 
ever, the nervous system appears to be very rudimentary. 
The sexes appear to be sometimes distinct and sometimes 
united in the same individual. The embryo, in some cases, at 
any rate, is locomotive, moving from place to place by means of 
the ciliated arms or by ventral spines. 
