IIVDROZUA. r»o 



from the p;ireut colony and swam away. In ibc <asf oi uian\ 

 Medusif, the eggs develop directly into Medusie, m. fixed su^^e " 

 being known ; here the Hxed stage, which there is reason to iK-lieve 

 has at one time existed in every case, has been *' hnrried throuj^h " 

 ill the egg. Medusai present two very dilVereut types of structure : 

 in (me, which may be called the " llydr<jmediis;in" type, the 

 umbrella is provided with a velum, tiie sense-organs are naked on 

 the umbrella margin (Naked-Eyed MediLsic), and the liied stock, 

 when known, is of the Hydra or Hydroid tyi»e, and jirtxluceg buds 

 laterally. Mediisaj of this type come under the sub-cla.ss Hydro- 

 mediisce, which includes Hydroida and Hydrocora/liiue. 



In Medusa? of the second or " Scyphomedusan " tyjK.- tlie 



Fi.;. 17.' 



'I\V 



(( 





fK 



J 



Female Medusa of ^lillepora, showing the eggs Am] lunrginal batteries 

 of thread cells. (After Prof. S. J. Hickson.) 



uml)rella is without a velum, the marginal sense-organs are coventl 

 by little lappets (Covered-Eyed Medusse), rows of " ga.stml fila- 

 ments " project into the stomach cavity, and the fixed stock. t»nly 

 known in a few cases, is a broad flattened polyp (8cyphi.stt)ma ^), 

 which produces buds by transverse fission (Fig. IHa-c), ami has four Case :i. 

 longitudinal ridges along the walls of the stomach cavity, Scypho- '^ l"""^''' I'*'"'* 

 medusan Medusa? are included in the sub-class Sryp/iumpdu.str. 



HYDROMEni'SAX ^IeduS/E. The tiny ^fedusiv given otT fnun the 

 fixed stocks of llydroid Zoo])hytcs come under two groups. Tliose 



' From " Proceedings^ of the Koyal Society." 

 - Skup]ios, a cup ; sto7na, mouth. 



