m COELENTERATA 49 



Class II. Scyphozoa. — Coelenterates in wiicli the dominant 

 phase is the " Medusa " or " Jelly-fish." The medusa may develop 

 direct from a fertilised egg, but in most cases it is formed by the 

 repeated transverse division of a small hydra-like but wide- 

 mouthed " scyphistoma." The sexual cells are discharged first 

 within the body-cavity. 



Aurelia, with medusa formed from a scyphistoma. 

 Pelagiii, with medusa developing straight from the egg. 

 Class III. Anthozoa. — Polyps in which the mouth-tube is 

 inverted to form the gullet, and the body-cavity is also partially 

 divided by radial mesenteries. In many, a solid calcareous 

 skeleton is laid down in the tissues of the body- wall. 



Sub -class A. — Polyps with tentacles six in number, or a 

 multiple of six. 



(1) Sea-anemones. 



(2) Stony corals, e.g. Devon Cup Coral and Madrepores. 

 Sub-class B. — Polyps with only eight-plumed tentacles and with 



no calcareous septa supporting them, but with an axial 

 rod-like skeleton, which may be rigid or flexible, formed in 

 the common axis of the skeleton, e.g. Corallium rubrum, the 

 Red Coral. 



Peactioal Work on Anthozoa 



Even if a student is living away from the sea and therefore 

 cannot study the creatures in the most desirable way, i.e. in their 

 own natural habitat, he may still make valuable observations by 

 keeping common Sea-anemones in a small sea-water tank. 



How to The " tank " may be merely a deep earthenware 



start a Sea- basin, glazed inside, or a large glass bell jar with a 

 water Tank, wide mouth ; but a rectangular tank, all glass, or one 

 made so that its joints will withstand the salt water, is desirable 

 when possible.^ 



Having obtained a tank, well-washed sea-sand or shingle 

 should be put over the bottom of it to the depth of about two 

 inches. It is very important that this should first be well washed 

 in a basin under a running tap until the water which runs off 

 it remains quite clear, then it must be well dried, or washed 

 once in sea-water, before putting it into the tank ; above this 

 shingle floor some kind of rockwork should be built up, so that 



^ Directions for starting a mariue aquarium are given in the penny Handbook 

 to the Marine Aquaria, to be obtained at the Horuiman Museum, Forest Hill, 

 London, S.E. A simple, easily made, little apparatus for keeping the water 

 always well aerated is described and illustrated in this guide. 



VOL. I E 



