82 INTRODUCTION. 



SUB-KINGDOM ILCCELENTERA TA. 



Animals whose alimentary canal communicates freely with the general 

 cavity of the body ; body composed essentially of two layers or mem- 

 branes, an outer layer or " ectoderm," and an inner layer or " endoderm." 

 No circulatory system or heart, and in most no nervous system. Skin 

 furnished with minute stinging organs or "thread-cells." Distinct re- 

 productive organs in all. 



CLASS A. HYDROZOA. Walls of the digestive sac not separated from 

 those of the general body-cavity, the two coinciding with one another. 

 Reproductive organs external. 



Sub-class I. HYDROIDA (Hydroid Zoophytes). 



Order 1. Hydrida. Ex. Fresh-water Polype (Hydra). 

 Order 2. Corynida. Ex. Pipe-coralline (Tubularia). 

 Order 3. Sertularida.Ex. Sea-firs (Sertularia). 

 Sub-class II. SIPHONOPHORA (Oceanic Hydrozoa). 

 Order 4. Calycophoridce. Ex. Diphyes. 



Order 5. Physophoridce. Ex. Portuguese Man-of-war (Physalia). 

 Sub-class III. DISCOPHORA (Jelly-fish). 



Order 6. Medusidce. Ex. Trachynema. 

 Sub-class IV. LUCERNARIDA (Sea-blubbers). 

 Order 7. Lucernaridce. Ex. Lucernaria. 

 Order 8. Pelagidce. Ex. Pelagia. 

 Order 9. Rhizostomidce. Ex. Rhizostoma. 

 Sub-class V. GRAPTOLITID.E (extinct). 



Sub-class VI. HYDROCORALLIN^E. Ex. Millepora, Stylaster. 

 CLASS B. ACTINOZOA. Stomach opening below into the body-cavity? 

 which is divided into a number of compartments by a series of vertical 

 partitions or " mesenteries." Reproductive organs internal. 



Order 1. Zoantharia. Tentacles simply rounded, in multiples of 

 five or six. Ex. Sea-anemones (Actinidse), Star- 

 corals (Astrseidse), Brain-corals (Meandrina), Madre- 

 pores (Madreporidse). 



Order 2. Alcyonaria. Tentacles fringed, in multiples of four. 

 Ex. Dead-man's-toes (Alcyonium), Organ-pipe Coral 

 (Tubipora), Sea-rods (Virgularia), Sea-pens (Penna- 

 tula), Red Coral (Corallinm), Heliopora, Heliolites. 

 Order 3. Rugosa (extinct). 



Order 4. Ctenophora. Animal oceanic, swimming by means of 

 bands of cilia or " ctenophores." Ex. Pleurobrachia, . 

 Venus's Girdle (Cestum). 



S UB-KINGDOM III. A NX UL 01 DA . 



Animals in which the alimentary canal is completely shut off from the 

 general cavity of the body, and in which there is a distinct nervous 

 system. A true blood-circulatory system may or may not be present. 

 In all there is a peculiar system of canals, which usually communicate 



