U THE YOUNG XATUEALIST. 



and which is very like the common jelly fish you 

 see floating about on the sea, and indeed many of 

 these have been proved to be the young forms of 

 the adult fixed Hydroida we are speaking of. 



The second class fStpTtonophbraJ are all free- 

 $wimming animals in tropical seas ; they are 

 something like those jelly-fish which everyone sees 

 at the seaside, but underneath they have clusters 

 of polyps like the simple Hydra. These have 

 the mouth downwards and are kept on the sur- 

 face of the sea b\* the sort of bladder-like float 

 from which the polyps are suspended. The 

 class (Disooplwm) includes the jelly-fish, but it is 

 questionable whether all these are perfect 

 animals, or only immature forms of other members 

 cf the grvr.p. The fourth cla^s (Lncinario?) are 

 in form something like the Hydra, but they can 

 detach tlncmselves and travel about at will. . In 

 their immature stage they are much like the jelly- 

 n>h. ar. ne larval il.nn discovered. I think during 

 the early part of the " Challenger " voyage was 

 7ft. across, and the tentacles which hung down 

 were 50ft- long, yet it was found out that this was 

 only the young stage of a Lucinarian, which 

 when properly developed was only half-an-inch in 

 height. There is another class called Graptali- 

 tidm, but they are extinct, being only found in a 

 fossil form, imbedded in the rocks. The second 

 division (ActiMma) differ from the first in this 

 respect. Suppose you take one, a sea anemone 

 for instance, and cut it horizontally across about 

 the middle, you will see a number of partitions 

 ivbieh radiate from the outer circumference to- 

 wards the central body-cavity, like the spokes of a 

 wheel. The cavities enclosed between these par- 

 titions communicate with the tentacles, many of 

 which have a little hole at the tip through which 

 4-he water can be squirted. The first class 

 {Zoantlmria) is made up of the sea anemones and 

 coral polyps. The sea anemones may be seen in 

 any rocky place around our coast, they are solitary 

 and do not build up structures like the polyps. A 

 heat of 66 degrees is necessary to the existence of 

 the coral animal, and they therefore cannot live in 

 our seas. Their principle interest to us is the 

 vast structures which they build up, called coral 

 reefs ; you have all heard of — and perhaps some 

 of you seen — that vast structure on the east coast 

 of Australia, which is more than 1,000 miles long, 

 and from four to five miles in width. These little 

 coral animals have the power of secreting carbon- 



ate-of-lime from the sea water, and building it upj 

 into their system. It forms the skeleton and thej 

 coral branches go on growing like the branches of 

 a tree. When the coral is alive the whole mass is 

 covered by a fleshy substance which connects the 

 various polyps together, and which belongs to thej 

 community. There are different kinds of coralj 

 reefs, which may encircle an island or run alungj 



Fig. 25. 



shores of a continent. Fig. 25 is called a fring 

 ing reef, there is no deep water between the edg«! 

 of the reef (a) and the land (b) only a shallovj 

 basin. Outside the reef it is not very deep, pen) 

 haps 25 fathoms. Fig. 26 is called a barric 



Fig. 26. 



• - 



reef, the distance from the edge of the reef to t! 

 land is greater and the wnter both inside and o 

 side is deeper. Fig. 27 is called an atoll and h 



Fig. 27. jj 



no land in the centre only a circular reef witlM 

 M lagoon " in the middle. On such a reef as 'I ' 

 we often find palm trees and other vegetatB 



