3H 



Marvels of the Universe 



THE GREEN 



TKis Sea-Slug is little more than half 

 is slender, but along eacn side tnere is 

 colour according to the hue of the weeds 



EL^SIA. 



in inch in lenfith. Its green body 

 a fin-liUe expansion. It varies its 

 ipon which it is found. 



inch long — the common Sea Lemon 

 measures three or four inches — and 

 bright scarlet in colour ; consequently, 

 we find it feeding upon a red sponge. 

 Johnston's Sea Lemon is creamy 

 white in hue, and it feeds upon the 

 paler varieties of Crumb-of-bread 

 Sponge, which varies from white to 

 orange. Most of the Sea-slugs have 

 a pair of tentacles, or sense organs, 

 standing up on the back behind the 

 head, and these often bear ring-hke 

 plates which appear to be the sensitive 

 portions. At the other extremity of 

 the body there is mostly a flower-like 

 expansion, which consists of the gills 



spreading around an orifice. In a large number of species there are in addition a varying number 

 of filaments, which wave over the back and produce beautiful effects. Shakespeare speaks of one 

 wearing his heart upon his sleeve for daws to peck at ; many of these Sea-slugs perform a similar 

 physiological feat by wearing portions of their liver on the outside of their bodies. These filaments 

 are really offshoots or branches from the liver, and their often beautiful colours are due to their 

 food or to the presence of bile. There is a double advantage about this arrangement, for whilst the 

 practice of wearing the liver outside gives more room for the expansion of the stomach within, the 

 colour of the food consumed shows up in these appendages and so helps to make the slug less 

 visible. For example, some years ago I experimented amongst other species with a pale form of the 

 Plumed Eolis by putting it successively into glasses of sea-water, each containing a sea-anemone 

 of a distinct colour ; and as it fed upon these in turn it changed colour accordingly. Its back is 

 covered with several hundreds of filaments resembling the tentacles of the common Beadlet 

 Anemone ; and when it is at rest after a meal, with the body curled round, it looks exactly like the 

 anemone it has last eaten — having adopted that anemone's colour. 



Homberg's Triton is a very large species — four to eight inches long — and the outgrowths from 

 its sides take the form of circlets of plumes, each of which reproduces a small seaweed, whilst the 



warts on its back resemble the unex- 

 panded polyps of the compound animal 

 known as Deadman's Fingers, upon 

 which the slug habitually feeds ! The 

 Bushy-backed Slug, which is much 

 smaller — about an inch and a half long 

 — has flat side ornaments cut and 

 jagged into a close resemblance to the 

 red-brown seaweeds among which it 

 lives ; whilst the Crowned Sea-nymph, 

 which feeds upon zoophytes ;ind coral- 

 lines, has the same parts got up to 

 closely mimic the class of animals upon 

 [/!« Then. Can-ems. which it prcys. Indeed, most of the 

 Li 1 1 Lfc. toLi:,. Sea-slugs, different as they are in form. 



This Sea-Slug measures less than a quarter of an inch, but its trans- i i ^ ii 



parent yellowish-white, marked with brown and olive-green. makes i, a ^OlOUr and Omament, arC all mOre Or 



pielty object. It lives on seaweeds, and mimics certain zoophytes. leSS " gOt Up " On a mimetic basls. 



