Tank No. 1. 
29 
First of all it must be remembered that Corals and Medusae, for 
instance, can do very well without head and tail, arms and legs, fins or 
Fig. 39. Holothuria tubulosa, */3 nat. size. 
wings, and so can the Echinoderms. Still, 
the latter have a much more complex 
structure than the former. Even their 
outward form is most variable. Some are 
almost spherical (Fig. 36), others are flat 
like a leaf ( Palmipes , p. 4), others again 
star-shaped (Fig. 37 and 38); some are 
cylindrical, something like a cucumber in 
shape (Fig. 39); and lastly some have the 
form of a flower attached by a short stalk, 
and seem to possess sepals and petals (Fig.4 0). 
The skin of these animals contains a large 
number of different but regularly arranged 
calcareous plates. In the sea-urchins these 
plates are fixed together so closely, that 
the spherical body seems to consist of a 
solid inextensible substance; in the star¬ 
fishes the plates are more loosely connected 
Fig. 40. Antedon rosacea attached 
to a branch of Antipathes, 
1 , , 2 nat. size. 
