A Holothurian. 37 



a thin-walled crop or stomach, from which the coiled in- 

 testine takes its origin, and continues to its posterior open- 

 ing into the cloaca. After making a careful drawing, remove 

 the alimentary tract, cutting it just back of the stomach and 

 anterior to the cloaca. 



The Respiratory and Excretory Systems. Lying lat- 

 erally in the body-cavity are the two main divisions of the 

 many-branched respiratory tree. Each half of this organ 

 will be found to open directly into the cloaca, through 

 which it may receive fresh sea-water and become greatly 

 distended. 



Make a drawing of the respiratory tree and the cloaca. 



The Reproductive System. The ovaries and testes 

 superficially resemble each other. The sexes are separate. 

 The genital gland (ovary or testis) occupies a median 

 position in the upper part of the body-cavity, and is made 

 up of a multitude of delicate filaments which collectively 

 form a brush. The organ is divided into a right and into 

 a left half, and its duct leads directly to the opening already 

 noted, between the two uppermost tentacles. 



Make a drawing of the reproductive system. 



The Water-vascular System. In certain specimens 

 the circum-oral water-tube or ring-canal will be found to sur- 

 round the deeper portion of the oesophagus, and to give off 

 one or two large and elongated Polian vesicles. Commu- 

 nicating with the tentacles, the ring-canal gives them their 

 power of expansion, and it also gives off five radiating canals, 

 which extend over the body and supply the innumerable 

 ambulacral suckers. Elongated filiform ampulla are abun- 

 dant and hang from the inner surface of the body-wall. The 



