7 4 Part second. 



Many Echinoderms have a great capacity for regeneration. 

 If one breaks off one or more arms of a Starfish or Brittle-star 

 they rapidly grow again. True, a lizard can re-grow its tail after 

 it has been broken off; but the starfish-arms are capable of more 

 than merely growing out again. A separated arm is able to give 

 rise to the whole middle piece and the remaining arms, and as 

 long as the newly formed parts are still small we get the so-called 

 "comet forms". To break the arm off a Starfish may appear 

 to be a cruel form of torture, but it cannot be so, for otherwise 

 the animals would not do it of their own accord. For there are 

 Starfish which, without appreciating the efforts of the anti-vivisec- 

 tionists, practice vivisection on themselves. They break them- 

 selves into two nearly equal pieces, each of which proceeds to grow 

 into a perfect animal. This is a normal form of reproduction 

 called "Schizogony" which these animals make use of besides 

 the usual method by means of eggs. The Sea-cucumbers too 

 have a remarkable habit. When the water in which they are 

 living becomes foul, they throw out the whole of their intestines ; 

 but as soon as normal conditions set in again they regenerate them. 



A glance at the Starfish, Brittle-stars and Feather-stars shows 

 that the Echinoderms (like the Corals and Jelly-fish) are built 

 on a plan which is fundamentally different from that of the higher 

 animals such as insects or mammals. The plan on which these 

 latter are formed is well-known to be a bilaterally symmetrical 

 one, but that of the Echinoderms is radial. Their body is arranged 

 with the organs disposed about a central axis like the sepals, pedals 

 and stamens of a flower. If we make the comparison with a 

 five-petalled flower, we have the same number of radii, as those 

 which make up the fundamental plan of Echinoderm organisation. 

 It is however very remarkable that the young free-swimming 

 stages of this group (for they, too, enjoy this happy youth, before 

 changing into the creeping adult) are in no way radially sym- 

 metrical, but bilateral, like the higher animals. For a long time 

 this has given the zoologists food for thought, but of late the 

 development of Echinoderms has been of interest to them in 

 another respect. The very transparent eggs not only give an 

 insight into the finest processes of the commencement of em- 

 bryonic development, they not only supply the main material 

 for a close study of the problems of heredity, but it has also been 

 possible to cause the development of young Sea-urchins through 

 artificial parthenogenesis, that is, the replacement of normal 

 fertilization by a purely chemical process. 



The whole company about which we have been telling all these 

 tales, while neglecting our duty of introducing its members per- 

 sonally to the visitor, is to be found together in tank No. i. 

 Below is a list of their names arranged in famihes with notices 

 on their appearance, habits, special peculiarities, etc. 



