SYSTEMATIC SURVE Y—HYDROZOA. 172 
(2) Hydrophora,—Two types are included here. The first includes 
the Tubularians, Aydvactinza, and other forms in which the polyps are 
not enclosed in the protective perisarc which often surrounds the colony 
(gymnoblastic), and in which the free medusoid forms, when present, 
have their genital organs placed in the wall of the manubrium 
(Anthomedusz), and are furnished with ‘ 
ocelli placed at the base of the tentacles, 
ffydra and its allies may be included here. 
An unattached marine hydroid—Ayfolytus 
peregrinus—has been described, and as it 
bore gonophores it was obviously mature, 
which is doubtful as regards two other 
unattached forms, Protohydra leuckartiz and 
Halermita cumulans, which may turn out 
to be larval. The hydroid stages of Pelago- 
hydra and Margelopsés are free-swimming. 
Examples :— 
Syncoryne sarstz, the free medusoid of 
which is called Sarsza tubulosa. 
Bougatnvillea ramosa \iberates the 
medusoid Margelis ramosa. 
Cordylophora lacustris and Tubularia 
larynx have sessile gonophores or 
sporosacs. 
The second type includes Campanularians 
and Sertularians along one line; Halecids 
and Plumularians along another line. The 
protective perisarc surrounding the colony 
is continued into little cups (hydrothecz) 
enclosing the polyps (calyptoblastic). These < 
hydrothecze are stalked in Campanularians, 
sessile in Sertularians and Plumularians. 
The free medusoids have their gonads placed 
in the course of the radial canals (Lepto- 
medusze), and are either ‘‘ocellate” or 
“* vesiculate.” 
Examples :— 
Plumularia, with hydrothece on one 
side of the branches, and Sertudlaria, 
AI. 
with hydrothecze on both sides of the dL. 
branches. 
The Campanularian Odelia geniculata ic. 88.-—Graptolites. 
liberates the medusoid Odea gent- I. Monograptus. 
culata. II.’ Diplograptus. 
(2) EHydrocorallinze. —Colonial torms which 
suggest the Hydractiniz in their polymorphism and division of labour, 
but are distinguished by their power of taking up lime, and so forming 
‘*corals.” The colonies are complex and divergent, the reproductive 
persons are either sessile gonophores or simple medusoids. A/¢//egora, 
Stylaster. 
(c) Trachymedusze.—These exist as a rule only in the medusoid form, 
