100 



ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



type of hydnml without a hydrotlura is said to be gymnoblastic, in con- 



ihc calyptoblastic type in which a hydrotheca is present. 



l belongs to a group in which the Medusae (Fig. 41, B) 



tnportant differences from tliose of Obelia. (i) They are deep 



ied instead ot saucer-shaped; (2) the gonad (g) is situated not 



re. 



Fin. 41. 



Diagram In illiistr.it.' tin- distiiiLjuisliiiii; features of A, Gymnoblastic polyp; B, Anthomedusa ; 



|inlv|>; I >, I.i-ptninrdiis.i. K, (ionad; h, hydrotheca ; m, mouth; ps, pcrisarc ; 



. "iin. [In Figs. B and D the right half cf the figure is in the plane 



: ili.- 1. ft half is in a plane lirtwr. n two ra<lial canals.] 



rface of the umbrella but on the outer surface of the 

 inanuhrmm : (\] the sense -organs when present are usually in the form 



lit of simple eyes. Such a type of medusa is known as 



iO Anthomedusa (Fig. 41, II) in mntradistinclion to the Leptomedusa 



i|.hlied by Obelia. In the genus Tubularia the 



:tiii is apparent ly commencing to degenerate, as the 



