The purpose of this paper is to lay the basis for some serious work on comparative acarinology. For this purpose a restricted group, the family Acaridae, has been selected and a detailed morphological study based on approximately 40 species, representative of the various genera of the family, is presented. It is hoped that this will demonstrate more clearly than has hitherto been done the significance, from the standpoint of classification and phylogeny, of the principal morphological characters present in this group of animals. The classifications of previous workers, particularly that of Oudemans', are briefly reviewed and evaluated in the light of present findings; a discussion of the composition and inter-relationships of the various genera and higher groups is given; and finally a synopsis of the tribes and genera of the family Acaridae, based on characters believed to be of phylogenetic significance, is presented.
The subfamily Rhizoglyphinae is a group which was reclassified by the Russian Zoologist, A. A. Zakhvatkine, in 1937. As a result of his studies he became convinced that Oudemans' 1923-1932 classification of the Diacotricha was unstable and very artificial.
The internal morphology and histology of the adult Caloglyphus mycophagus is described from serial sections fixed in 10% acrolein and embedded in glycol methacrylate. The alimentary tract has a typical acarid form, characterized by a well-developed stomach bearing a pair of caeca, a distinct colon and rectum. A pair each of Malpighian tubules and salivary glands also are present. At least three types of cells are recognized in the wall of the stomach and caeca. The central nervous system comprises fused supra- and sub-oesophageal and ventral ganglia. The male reproductive system is characterized by the presence of asymmetrical testes and a single large median accessory gland; the gonads in the female are paired and symmetrical and a pair of accessory glands are present. Details of 11 pairs of body-wall muscles, 7 pairs of genital muscles, 3 pairs of excretory pore muscles, and a number of coxal, leg, and gnathsomal muscles are given. No tracheae nor spiracles were found, but one pair of oil glands is described. The thin cuticle consists of three layers. Attention is drawn to the anatomical differences between this species and other species and their functional significance is discussed.
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