CCtLEI^TERATA — CORALS 



127 



teries, and new tentacles, so the coral base enlarges in circum- 

 ference and new septa develop between the older ones, — six 

 in the first set, six in the second, twelve in the third. The ani- 

 mal thus impresses its growth stages from youth to maturity 

 upon its coral secretion, and accordingly we would look towards 

 the narrower end of the coral for the record of its youth. 



The basal portion of the polyp grows a very short distance 

 from the edge of the cup out over the shell or stone upon which 

 it is fastened; from this basal expansion bud up new polyps, 

 while from their basal expansions or from that uniting them 

 with their parent or each other, arise other buds. All these 

 finally develop into polyps capable of catching and digesting their 

 own food ; but until then, they grow through the nourishment 

 contributed by all the other polyps, for the digestive cavities 

 of all the colony are continuous with one another through these 

 basal expansions, — the common flesh, or ccenosarc. 



1. Examine Astrangia, noting the tentacles, mouth, oesoph- 

 agus, mesenteries and their relation to the septa, digestive 

 cavity, nettle-cells. 



2. Examine the sea anemone: {a) an entire specimen; 

 {h) an individual sectioned vertically through the mouth. 

 Note tentacles, mouth, oesophagus, mesenteries. 



3. What is the habitat of Astrangia ? 



4. Of what does its food consist ? How does it procure it ? 



5. What keeps the prey from struggling after being sw^al- 

 lowed, and thus injuring the soft body of its captor? 



6. Briefly describe the digestion of the food, excretion of the 

 waste and the method by which the nourishment reaches all 

 parts of the body. 



7. How does Astrangia breathe? 



8. What muscles are present ? Their use ? 



9. What is the function of the nerves ? 



10. What sense organs does it possess ? 



11. Describe the development of Astrangia from the egg to 

 adulthood, noting quite fully the development of the hard parts. 



12. What record of this development is present in the coral 

 secretion of an adult ? 



13. How does a single polyp become a colony ? 



