1880.] 407 [Hagen 
Class I. Galls with unlimited growth. 
Several generations of the tenants produce the gall, which was 
first began by a single full grown individual. Nutrition 
and propagation of the tenants take place in the gall. 
Order I. External galls. The tenants do not penetrate the 
plant with their body. 
Family I. Hemipterous galls, deformations of the 
leaves ; some tenants build dimorphous galls, on dif- 
ferent parts of the plant (Phylloxera, Brachyscelis). 
Group 1. Galls with centrifugal growth, simple or 
compound. ‘The gall develops in a direction 
away from the tenant (Chermes, Psylla). 
Group 2. Galls with centripetal growth (Pachy- 
pappa). : 
Family Il. Phytoptus galls, simple or compound. 
Order II. Internal galls. The tenants penetrate with the 
whole body into the interior of the plant, where nutrition 
and propagation takes place. 
Family I. Some Phytoptus galls. 
Family II. Anguillula galls. 
Class II. Galls with limited growth. One or more tenants inhabit 
the galls only during the period of development of the imago. 
Order I. Larva galls; ege deposited externally ; the larva 
penetrating into the plant. 
Family I. External galls, simple or compound (Ceci- 
domyia). 
Family II. Internal galls—or inflated mines, or swell- 
ings, or deformations of the flower or of the fruit, or 
entirely closed larva galls (Diptera, Lepidoptera, 
Coleoptera). 
Order II. Imago galls. The imago pierces the plant, and 
deposits the egg in its interior parts (Hymenoptera.) 
Family I. Tenthredinidae. 
Family II. Cynipidae. 
I have tried in the foregoing sketch to combine in some way the 
views of Mr. Beyerink with those of Dr. F. Thomas, given in the 
Jahresbericht and in some other papers. The principal division in 
the two classes accords, indeed, very well with a general classifica- 
tion of the galls from a zoological standpoint, but the growth of the 
gall in the first class is not always unlimited, and depends in the case 
