68 
MEMBRA GIDJE. 
PTERYGIA. 
Notwithstanding all that has been written, the doctrine that every organ of an 
animal has some connection with its beneficial economy must be put aside. A com¬ 
petent authority remarks, that not one of the higher animals can be named which 
does not show, in some part of its body, a rudimentary condition.* Yet the interest¬ 
ing fact remains, that even when an organ is prejudicial to the welfare of an animal, 
it is not necessarily suppressed. Apparently useless organs, like the mammae of the 
male, still persist through ages of possible modification. From the law of Causation 
we must infer that all effect is the result of purpose, unless we adopt the illogical and 
inefficient doctrine of Necessity. Intelligence, we may think, should not produce what 
we may conceive to be effete organs. Do we not thus argue from imperfect premises? 
Unfortunately, as to the development of the Membracidae, we are without any 
testimony of their existence in the rocks ; for they seem to contain no fossil remains, 
either adult or larval, to show us the processes of either evolution or degeneration. 
Yet there would appear to be no adequate reason why such forms should not figure 
in the great insect deposits of America, and particularly in those districts where the 
living insects are now so plentifully scattered. 
It has been said that no animal form which has once become extinct can again 
arise : this may be rather a hazardous statement to make.f The insect productions 
of East Africa, at one time supposed to be unique and peculiar to the island of 
Madagascar, can now be met with on the coast round about Natal and Zanzibar. 
To meet this and similar facts, Darwin explains that species that were once widely 
distributed, sometimes have suffered much extinction in their struggles for existence. 
Isolated species and genera, it is suggested, may thus be the sole existing remnants 
of a once numerous group. 
The extraordinary structural additions to the pronota of Pterygia and other 
genera are not confined to a few Membracidte developed in sporadic centres. They 
occur over wide areas, separated by deserts, seas, and mountain ranges. 
Genus : PTERYGIA, Laporte. 
Ann. Soc. France, i. p. 221 (1832); Fairm. l.c. p. 263; Stfil, Ofv. Vet. Akad. p. 276; Fowler, 
B.C.A. p. 23; Walk. List. Homop. ii. p. 499, Suppt. p. 127 ; Notocera. Amyot. et Serv. l.c. 
Hemip. p. 536. 
Head sloped (echancree) on each side and scooped; eyes large; ocelli placed close 
to the eyes, and near the prothorax ; pronotum rugose, tuberculate and generally 
* “Descent of Man,” vol. i. p. 17. 
f See this subject discussed by W. F. Kirby, “Evolution and Natural Theology,” p. 116 (1883). 
