296 TADPOLES OF THE SEA 



touch-sense of those creatures and their phenomenal skill 

 in spinning and construction, and have also become (no 

 doubt as an element of safety) extremely small. The 

 mites (cheese mites, bird and horse mites, itch insects, 

 and plant mites) are specialised and simplified spiders. 

 The vigorous and active organs of the spiders have in 

 them dwindled and to a great extent atrophied. They 

 are instances of simplification connected with the specialism 

 which secures them abundant food and safety in virtue of 

 their small size and capacity for sucking nutriment from 

 all sorts of obscure sources where they find no competition. 

 A few words must now be said about the exquisitely 

 beautiful creatures to which the Ascidian race has given 

 rise creatures which are amongst the most curious, and 

 at the same time the most gem-like in colour and trans- 

 parency, of all the myriads of lovely things which the 

 everlasting ocean offers to our eyes. The common large 

 Ascidian, two inches or more in length, is a rough- 

 looking, oblong sac, securely fixed by an adhesive base to 

 a rock. Suppose this base to grow and spread over the 

 rock and to give rise to buds like the stem of a plant, so 

 that several Ascidian sacs are produced resting on an 

 enlarged base ! That seems an incredible thing for an 

 animal to do and more like the growth of a plant but it 

 is the regular mode of growth in some Ascidians. Then 

 suppose that the sacs are not large and coarse, but only 

 as big as a large dewdrop, each like a goblet in shape and 

 perfectly transparent and colourless, as though carved in 

 rock crystal. This being accomplished, you have the little 

 compound or budded Ascidian called " Clavelina " ! It 

 is a marvellously beautiful thing, and groups of them 

 may often be found on rocky shores at very low 

 tide, attached to the under-surface of ledges or slabs 

 of rock. Its crystal-like transparency not only makes 

 it a wonderful sight to the unaided eye, but enables 



