30 BRITISH OAK GALLS. 
conveying to the embryo a supply of oxygen which 
otherwise could not reach it. 
The larve are fat, fleshy, and legless, white or 
cream colour. When removed from the larval cell and 
placed ona flat surface they will remain almost inactive. 
They lie within the larval cavity with head and tail 
directed slightly towards each other along the ventral 
surface. The body has thirteen segments. The 
mandibles are short, broad, and sharply cusped. They 
pupate in the galls without exception. The length of 
time required for development is variable. Nothing 
passes through the body. 
The pupa is the same colour as the larva, until 
shortly before the emergence of the imago, when it 
changes to a deep pink, the eyes become distinct and 
the appendages also. The antennz and legs are 
enclosed in pellicles, and are placed along the ventral 
surface of the thorax; the wings are like small bags 
placed on the sides of the thorax. 
The most wonderful features connected with the’ 
life-history of this family of gall producers are the 
alternations of generations, sometimes also called hetero- 
genesis, in which the young do not resemble their parent, 
Dut their grand-parent ; and parthenogenesis, or virgin 
production. Thus these insects, although somewhat 
insignificant in appearance, are of extreme scientific 
interest on account of the alternations which the 
various broods present of winged or wingless, and 
sexual and sexless, individuals at different times of the 
ear. 
y The phenomenon of alternating generations is not 
confined to the Cynipide. It occurs in the Salpinide ; 
among some species (the liver-fluke) in the parasitic 
Entozoa; it is also one of the means of propagation 
among the Hydromedusz and the Polyzoa. 
Dalbert de Chamisso was the first to observe this 
phenomenon, when in 1815 he accompanied, as natura- 
list, an expedition round the world. 
His observations, published in 1819, were not believed, 
