OF SOUTIIERX IXT)L\. 
o 
or more twists, and is attached to the inner wails of tlic test by numerous fine 
muscles. Xo special secretionary organs arc known, and in many instances it is 
yet very doubtful what should be regarded as organs of respiration. Some of the 
Echiuoidea have the peristome with two incisions in each intcr-amhulacrum, and 
through these incisions certain hranched organs are protruded, wliich arc at least 
partially supplied witli vessels, and, therefore, regarded as buccal gills. Other 
morphologists attril)utc to respiratory functions cei’t^in pedicells which are protrud- 
ed through the amhulacral pores, and which are partly peculiarly shaped. These 
pedicells will be alluded to again hereafter. As, however, all these organs have 
only a limited extent, and are in some Echinoids entirely al^scnt, it is commonly 
believed that respiration is maintained liy the entire inner side of tlic body, the 
movement of the water which enters through the mouth being facilitated by the 
constant motion of the cilia of the inner epliithelium. 
In connection with the respiration may be mentioned the peculiar aquiferous 
system, which is, as in the Asteroidea, of very considerable extent. It begins with 
the madreporiforin plate, a finely porous calcareous disc, situated in or near the 
apex, and often grown to the right anterior genital plate. From the madreporiform 
plate leads a rather fine and thin dermal tube to the so-called circular canal, 
internally supplied with cilia and surrounding the oesophagus. Besides several 
smaller cellidar enlargements, five long, again sub-divided arms branch off along the 
inner ambulacral walls and partially terminate in the pedicells, protruding through the 
ambulacral pores. These pedicells are generally peculiarly formed, with thickened, 
soft terminations, undulating at the margins. There are, however, many other 
kinds of pedicells round the mouth and on different portions of the body, some 
with globular ends, others branched, and again others with regular small suckers, 
supplied with numerous calcareous paidicles. They arc believed to perform different 
functions, some being particularly destined as organs of the touch, others of locomotion, 
or for temporary attachment, etc. In addition to these there are the pedicellarioe, 
which appear to be special epidermal organs, consisting of a short stem and three 
terminal branches, which act as nippers ; they are partially of solid structure, and 
probably intended as prehensile organs. They re-call the form of the so-called 
avicularia of the Ciliopods (Bryozoa). 
The centre of the circulatory system of the blood is a heart, which is an 
elongated, .somewhat tAvisted canal, situated near the cesophagus, above the jaAVS. 
It sends one anterior arterial branch towards the mouth, near which it forms a 
ring, sending off branches to the muscles of the lanterne and the other parts of the 
body, and posteriorly it receives a venous arm, which, after receiving through a 
capillary system the chylus from the intestines, conveys it to the respiratory 
epithelium of the inner walls of the body and then to the heart. 
The nervous system consists of a ring round the oesophagus, from which fiA^e 
principal ambulacral nerves branch off, being again numerously sub-divided and 
supplying the other organs. Each of the branches terminate AA'ith a thicker ring, 
( 75 ) 
