HTDROZOA. 79 



Section HI. 



CLASSIFICATION OF HYDROZOA. 



I. Classification. — 2. Order i: Hydridae. — 3. Order 2: Corynidae. 

 — 4. Order 3 : Sertularidae. — 5. Order 4 : Calytophoridae. — 6. 

 Order 5 : Physophoridae. — 7. Order 6 : Medusidae. — 8. Order 7 : 

 Lucernaridae. 



I. ClassiHcatioiB. — The seven orders into which 

 the class Hydrozoa is divided may be defined as 

 follows: 



1. Hydridce. — Hydrozoa, whose hydrosoma con- 



sists of a single locomotive polypite, wdth 

 tentacles, hydrorhiza, and reproductive organs 

 which appear as simple processes of the body- 

 wall. 



2. Corynidce, — Hydrozoa, whose hydrosoma is 



fixed by an hydrorhiza, and consists either of 

 one polypite, or of several connected by a 

 coenosarc, which usually developes a firm 

 outer layer. Eeproductive organs in the 

 form of gonophores, which vary much in 

 structure, and arise from the sides of the 

 polypites, from the coenosarc, or from gono- 

 blastidia. 



3. Sertularidce. — Hydrozoa, whose hydrosoma 



is fixed by an hydrorhiza, and consists of 

 several polypites, protected by hydrothecse, 

 and connected by a coenosarc, which is usually 

 branched, and invested with a very firm outer 

 layer. Eeproductive organs as gonophores, 

 arising from the coenosarc, or from gonoblas- 

 tidia. 



