54 ZOOLOGY 
mentary tentacles may occur on the gonophore. As stated 
above, the medusoid persons in Zubularia do not break away 
or develop further. The gener- 
ative organs are found on the 
walls of the manubrium (Fig. 39, 
II.), the medusoid persons bearing 
either male or female cells, but 
Fic. 40.—Diagrams of the forma- not both. 
tion of Medusae by budding. In those species in which 
2 hihater | er peace teen the medusoid person is completed, 
as in Fig. 89. The Coelenteron other structures develop; ten- 
is black. After Korschelt and 
Heider tacles and sense organs arise 
I.—Commencement of bud. round the edge of the umbrella, 
a muscular fold, the velum, is 
formed inside the rim of the um- 
brella (Fig. 40, IV.) and functions 
as a swimming organ, and the 
medusa breaks away and swims 
freely through the water. The 
existence of these two phases in 
II,.—Thickening of ectoderm and the life-history of one organism 
cupping of endoderm. has rendered necessary a double 
classification. The order to which 
Tubularia belongs is the Gymno- 
blastea-Anthomedusae : the first 
word referrmg to the nature of 
the hydroid form, the second to 
that of the medusoid. 
Order 1. 
Gymnoblastea-Anthomedusae. 
IIJ.—Formation of sub-umbrella cav- 
ity in the ectoderm. 
CHARACTERISTICS.— These HHydro- 
zou have probably always a 
hydroid stage, which is very various in appearance, sometimes 
non-colonial, but more usually the hydroids are united into 
colonies. The ectoderm may form a _ perisare, but this 
is never continued into a cewp or hydrotheca surrounding 
