The relationship of book lung and tracheal systems in the spider family uloboridae.

The book lung surface areas of representatives of six genera were measured and divided by spider prosomal and leg mass and by the product of prosomal length and width to obtain two indexes of book lung area. Both indexes are greatest in species that have the simplest tracheal systems and smallest in those with the most extensive tracheal systems. When species are ordered phylogenetically and the lung area indexes of their hypothetical ancestors computed, a transformational increase in lung area is indicated. Neither the lung area of a species nor its phylogenetic position is significantly related to the general moisture regime of its habitat. The number of leaves in a book lung is positively correlated with both spider size and total lung area. However, leaf number is not correlated with tracheal development and shows no transformational change.