Concentration of the organ-systems by fusion of neighbouring regions (prosoma, mesosoma, metasoma), pre viously distinct, has frequently occurred, together with obliteration of the muscular and chitinous structures indicative of distinct somites.
This concentration and obliteration of somites, often accompanied by dislocation of important segmental structures (such as appendages and nerveganglia), may lead to highly developed specialization (individuation, H.
Pology, Cambridge, 1904, p. 98), it is fairly clear that the human liver is formed, not by a suppression of any of the lobes of the generalized type, but by a fusion of those lobes and obliteration of certain fissures.
Tentacles are hollow; but in some cases the tentacle may become solid by obliteration of its cavity.
Of the highly developed civilizations which grew up and flourished in Bactria, Bokhara and Samarkand the last survivals are now undergoing rapid obliteration with the simultaneous desiccation of the rivers and lakes.