ffnr.oTnrrfUAys. 



177 



There is no dental Mjipnratus in Ilic lioldtliiiriils, l>ut, a slidrt [iharviix Icarls into a 

 stomach, and this into an intestine nsnally much longer than the hodj-, and often 

 several times its length. In the 

 higher holothurids the intestine 

 terminates in a distinct chamber 

 < ir cloaca, often of large size. Into 

 this cloaca open the stems of two 

 (sometimes one) hollow, much- 

 hranched organs called the'res- 

 ](iratory trees.' The sea-water 

 enters into and is expelled ont 

 of these' organ.s, which thns fill 

 the body-cavity with water that 

 is taken up by the madreporic 

 body and carried Into the water- 

 system. The respiratory trees 

 are also believed to be organs of 

 excretion. 



In some holothurians the 

 cloaca or the respiratory tree is 

 also jn-ovided with sim])lc or 

 branched appendages the interior 

 of which is occuj)ied by a solid 

 nr viscid substance. The use of 

 these is not certainly known, but, 

 as they are readily thrown ont 

 when the animal is disturbed, 

 Semjier supposes that they are 

 <irgans of defence. These are 

 known as the Cuvierian organs. 



The nervous system is of the 

 usual echinoderm pattern, consist- 

 ing of a mouth-ring 2)laced above 

 the ring-canal of the water-system, 

 and of five principal ambulacral 

 cords passing through notches in 

 the plates around the a?sophagus. 

 The system which is sujjposed to 

 be analogous to the circulator}- 

 system of higher animals is very 

 complex in many of the higher 

 holothurids, extends over the ali- 

 mentary canal, and enmeshes one 

 of the respiratory trees. 



The genital organ is in many- 

 cases single, and in the Synap- 

 tidfe contains both ova and sper- 

 matozoa, so that these forms are 



VOL. I. — 12 



Fio. 156. — Anatomy of fnutliiui annata; a, anastomoses of dorsal 

 blood-vessels; //.branchial tree; f/, dorsal blood-vessel; /, mesen- 

 terial filaments; ,f7, genital opening; /, alimentary canal; /.longi- 

 tudinal nuiscles; m, mouth; o, genital duct; p, pharyngeal ring; 

 r, reproductive organs, cut away on right side; t, tentacular am- 

 pullse; V, ventral blood-vessel, 



