2 i2 THE BOOK OF NATURE STUDY 



oldest inhabitants. The connection between ants and pheasants 

 may be inquired into. 



Oak - Galls. The wood excursion should include the ex- 

 amination of some galls an interesting subject from the " Nature 

 Study " point of view, since it illustrates the interlinking of plant 

 and animal life. In the case of the common " marble-gall " 

 which is a good one to start with the gall is the result of an 

 interaction of the living cells of the oak-bud on the one hand and 

 of the larva of the gall-wasp on the other hand. The secretions of 

 the larva seem to stimulate a peculiar, but most orderly growth 

 on the part of the oak, and the result is an excrescence which 

 affords readily available food for the larva, and is also beneficial 

 to the plant, since it localises the injury inflicted. 



The marble-gall is often about an inch in diameter, and is 

 usually smooth, as its name suggests. It is green in summer, 

 and then turns brown. The larva, which is found in the centre, 

 is white, footless, and fleshy, with thirteen segments. The adult 

 insects, which hatch out at different times, are small reddish yellow 

 Hymenoptera (Cynips kollarf). 



The oak-spangles (Neuroterus), which occur on the under side 

 of oak leaves as small lens-like or saucer-like bodies, are due to 

 the larvae of a small cynipid. If the larvae develop into adults, 

 these form galls of another kind, so called currant-galls, pea- 

 shaped, glossy, green often with red spots to which a different 

 name (Spathegaster) was given before it was known that the life- 

 history of this and many other cynipids included two different 

 forms of gall and two different forms of adult insect. What come 

 out of the spangle-galls on the leaf (all females) deposit eggs in the 

 bud, and the resulting larvae form currant-galls. What come out 

 of the currant-galls are males and females, and the female deposit 

 eggs in the leaf, and the resulting larvae form spangle-galls. 1 



Wood-Lice. Attention should be paid to the wood-lice, or 

 " slaters/' of which there are many kinds, Porcellio scaber one 

 of the commonest. They are interesting in many ways, because 

 they are terrestrial Crustaceans which have left the aquatic home 

 of their race ; because they have a peculiar adaptation to breathing 

 dry air, namely, tubular passages in some of their limbs ; because 



1 See (Gillanders) p. 222. 



