QUESTIONS ON THE CffiLENTESATA. 259 



24. What genera of Coelenterata are known to inhabit fresh water ? 



25. Give some account of the geographical distribution of the Sertu- 



laridse. 



26. Describe the minute structure of the bod}'- wall in Actinia. 



27. What law appears to determine the number of parts among the 



several orders of Actinozoa ? 



28. What is the number and structure of the tentacles in the 



Alcyonaria ? 



29. Describe the structure of a typical ' corallite.' 



30. Define the order Rugosa, 



31. Explain the formation of the gyrate corallutn of Mceandrina. 



32. How does a ' sclerobasis ' differ from a true corallum? 

 33 Compare the nutrient system in 



a. Actinia and Pleurobrachia. 



b. Pleurobrachia and Beroe. 



34. Describe the structural relations of the tentacles in 



a. Actinia ; 

 h. Cestum; 

 c. Pleurobrachia. 



35. What characters distinguish the thread •cells of the Cteno- 



phora ? 



36. Describe the structure and position of the ' ctenocyst.' 



37. Give some account of the nervous system of the Ctenophora. 



38. What peculiarity of position distinguishes the reproductive 



organs of Tubipora ? 



39. Define precisely the position of the male and female organs iu 



the Ctenophora. 



40. What, according to Haime, is tlie number and succession of the 



tentacles in the common Sea-anemone ? 



41. Give some account of the development of the canal system iu 



Beroe. 



42. What numerical law governs the development of the ' septa ' in 



a Zoantharian corallite ? 



43. Distinguish three principal modes of gemmation among the co- 



ralligenous Actinozoa. 



44. Describe the structure of a Fringing-reef. 



45. How has Mr. Darwin explained the true nature of Barrier-reefs 



and Atolls ? 



S 2 



