STARFISH 111 



h. The heart. — How does it compare in size with the 

 stone canal? Kemove the heart from the body 

 and examine under the low power of the micro- 

 scope. What is the structure of the heart ? 

 By injecting into the pericardium with a fine syringe 

 a colored fluid, such as water containing carmine or in- 

 digo, the course of some of the peri-hsemal tubes 

 which surround the true blood-vessels may be made 

 plain. It will then be seen that there is (1) a circum- 

 oral peri-hsemal tube surrounding the mouth just be- 

 low the circum-oral water-tube ; (2) a radial peri-hse- 

 mal tube running from (1) to the tip of each ray, like- 

 wise just below the radial water-tube ; (3) a circum- 

 anal peri-haemal tube, which is on the inside of the 

 aboral surface of the disk, and is larger than the peri- 

 haemal tube around the mouth. Its branches run to the 

 aboral end of the pericardium, the stomach, the hepatic 

 cceca, and the reproductive organs. 

 Make a diagram of the circulatory system. 



E. — The Respiratory System. 

 Kemove a piece (about one-half inch square) of the aboral 

 wall of a ray, and carefully examine under water 

 the depressions on its inner surface. Look for 

 small openings in these depressions, and try to see 

 if these openings bear any relation to the aboral 

 tentacles on the outside of the ray. If necessary, 

 use a fine bristle. Try to pass the bristle through 

 one of the openings to see if the latter communi- 

 cate with the tentacles. Carefully peel off the lin- 

 ing membrane. What effect has this operation on 

 the tentacles 1 Notice that a tough membrane con- 

 taining the ossicles remains. In the same manner 

 remove the covering membrane on the outside. 



