QUESTIONS ON THE C(ELENTERATA. 259 



14. What genera of CoDlenterata are known to inhabit fresh water? 



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



1 arid IB. 



26. Describe the minute structure of the bodj'-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 Kuiijosa. 



31. Explain the formation of the gyrate corallum of Moeandrina. 



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

 33 Compare the nutrient system in 



o. Actinia and Pleurobrachia. 

 b. Pleurobrachia and Beroe. 



34. Describe the structural relations of the tentacles in 



a. Actinia; 



b. 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 in 



the Ctenophora. 



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



tentacles in the common Sea-anemone? 



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



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 ? 



S2 



