of them have lived and worked in Europe, and consequently the mite fauna of that continent is much better known than that of any other. The student intending to prosecute intensive research in this group should first thoroly acquaint himself with Canestrini's "Prospetto dell' Acarofauna Italiana", and follow this with an exhaustive review of the numerous and valuable contributions of a later Italian worker, Antonio Berlese. The works of C. L. Koch, P. Megnin, E. L. Trouessart, F. Koenike, L. G. Neumann, P. Kramer, I. Tragardh, S. Thor, A. Nalepa, and A. C. Oudemans of the continent and A. D. Michael, S. Hirst, and G. F. Nuttall of England are invaluable to students of acarology in the respective fields of each of these authors. In the United States there are four individuals who have contributed in a comprehensive manner to the knowledge of our Acarian fauna; Dr. H. E. Ewing of the National Museum and Dr. Nathan Banks of Harvard University, working in the terrestrial groups; and Dr. Ruth Marshall of Rockford College and Dr. Robert Wolcott of the University of Nebraska, undertaking the study of the aquatic mites. Dr. Banks and Dr. Wolcott are no longer engaged in active work on the Acarina.

Having spent much time during the last several years in the field study of insects, I became interested in our minute mite fauna, which is often very closely linked with the insect fauna. The subject being but slightly investigated, I was led to present this introductory study of the Acarina of Ohio.

The collections of Dr. H. Osborn, the Ohio State University, and the Ohio Experiment Station yielded scarcely 75 slides, many of which were rendered useless because of the deterioration of the mounting medium. A general collection of 25 slides made by C. K. Brain at Cedar Point, a few records of Eriophyidae by Cook and Wells, and a few new species and others recorded by Dr. Ewing formed the basis of this work. The entire literature did not comprise more than 100 pages. This should not lead one to conclude that the mite fauna of Ohio will be found totally different from that found elsewhere in the Austral Zone. My personal collections and notes were made over a period of several years with Chillicothe, in south-central Ohio, as the locality. In this discussion I shall review the technique usually employed in acarology and present those forms known to Ohio with such notes as will enable one to more easily recognize them.

Before continuing with this subject I wish to acknowledge my indebtedness to Dr. Herbert Osborn, Dr. H. E. Ewing, Dr. Ruth Marshall, Dr. R. C. Osburn, and Prof. H. A. Gossard for the

encouragement each has given me and for the specific manner in which each has further contributed to whatever merit this paper may possess.

METHOD OF APPROACH

Any investigator appreciates the value of as extensive a library as the means at hand will permit. Because of the comparatively small volume of literature dealing with the fauna of the United States it was not difficult to secure the more valuable contributions to acarology. Access to several of our larger libraries made accessible the more important foreign contributions. A card bibliography of all literature dealing with the Acarina, altho not complete, comprises upwards of 6,000 references. This will at once suggest the difficulty confronting anyone endeavoring to place all the literature of this group within one library.

To become the master of an order in the plant or animal kingdom has ceased to be within the realm of possibility for most individuals. With few exceptions an order includes such a diversity of forms with such varied habits that most workers must be content with the acquisition of a general knowledge of the entire group and, in the course of time, with the isolation of some smaller portion upon which to focus a more detailed study. The Acarina, constituting a very large order, must of necessity be attacked in this manner. Thus far I have made collections to the extent of more than 1,000 slides. This material represents many families in all of the seven superfamilies. Such a range evidences the method used in collecting, and reference to the habitat notes accompanying each species will throw further light upon the source of material. For one desiring a broad general knowledge of the Acarina such a random collection over several years will serve admirably.

After having isolated several species upon which to center special study, it was the program of each collecting trip to carefully examine the bark crevices on trees; the areas beneath fallen debris of all kinds; the areas beneath loose bark; the galleries of burrowing insects and rodents; the malformations and discolorations of leaves, flowers, and fruits that might come within range of the eye; and all insects or other animals that could be caught, as these might harbor parasites. Many species are also of common occurrence in food products, whether stored or offered for sale, and in clothing, furniture, etc., while others frequent decaying material of various kinds. Several large groups, found as parasites on the more elusive animals and undoubtedly well represented in Ohio,

are not recorded here because I, as others, have not taken the time necessary to secure them. Aware of the rich aquatic fauna present in adjoining states, I made a short collecting trip to Buckeye Lake in Ohio and there captured most of those aquatic Acarina herein recorded.

The technique involved in preservation and preparation for study is still far from perfected for all groups. When living specimens are to be mounted they may be killed in hot water, which usually leaves the appendages extended. Dehydration and mounting in several different media, depending upon the chitinization of the integument, then follows. For those heavily chitinized forms, such as adult Oribatoidea, Parasitoidea, Ixodoidea, and the like, a good grade of Canada balsam answers very well. The fact that this medium darkens with age is one serious objection to its use. For soft bodied species balsam has that undesirable property of causing the body to shrink and thus obscure many of the more minute characters. Sodium silicate has been suggested to eliminate this difficulty but, after examining some material mounted in this medium, I cannot recommend it as suitable except for temporary mounts.

A medium that I have used with considerable satisfaction for all forms is glycerine jelly. This is composed of 50 cc. of glycerine, 42 cc. of water, 6 cc. of melted or dissolved gelatin, and 2 cc. of carbolic acid. The latter serves to destroy any fungus organisms that might otherwise find the material a suitable culture medium. A small well approximately the diameter of the cover glass to be used is made on the slide with gold size. It is well to prepare a large number of these in advance so that they may become thoroly dry before being used. I have found that this material preserves the natural color of the mite for some time; it does not cause shrinking of the body; the appendages are nicely distended, altho the specimen has not been killed in hot water; and the mite remains soft and easily manipulated, if such be necessary. The sole objection that I have found to glycerine jelly after several years of use and an examination of many mounts of other workers is the necesity of protecting it against slow evaporation. After the cover glass has been put in place the slide is set aside to dry. When the jelly has set and the cover glass edge is dry a ring of damar varnish, white lead, or some other suitable material is run around it. If the material is thin this may have to be repeated. As this ring hardens it develops minute cracks and pores thru which the glycerine preparation slowly evaporates. Slides prepared by some of our

most exacting technicians have not been free from this difficulty. It is therefore necessary to examine glycerine mounts at least once each year and to apply a fresh layer of the ringing material to those showing any deterioration. It may often be found necessary to remount some valuable specimens because deterioration has progressed to such an extent that mere reringing will not prevent their loss.

Some mites may be successfully cleared in warm KOH and then stained as is the practice with the Coccidae. So little has been done with this method that details will be omitted here. Euporal has been used to a slight extent and seems to be as satisfactory as balsam. Gum arabic is sometimes added to the glycerine jelly to give it more body. Time alone will prove or disprove the value of these materials.

Where possible duplicate material should always be preserved in vials. A 75 or 85 percent alcohol has long been the standard material to use. All workers soon learn that alcoholic material is hard and in time becomes colorless. Thru evaporation many valuable collections preserved in alcohol have been lost. Wishing to eliminate as many of these faults as possible, I have employed a mixture of 1 part glacial acetic acid, 1 part glycerine, and 1 part water as a preserving medium. I believe it to be preferable to alcohol in several respects: the specimens remain soft and pliable; retain their color for a considerably longer time than those in lcohol; and altho evaporation takes place, it does so but slowly and thus decreases the possible loss thru this channel.

Altho it may seem needless to emphasize the accurate and complete labeling of slides and the maintenance of accurate and detailed notes, I take this opportunity to do so, prompted by the difficulties that I have experienced in studying many slides whose value was small due to a lack of adequate data.

In field collecting I have found a fine brush or a moistened splinter to serve adequately in picking the mites from their habitat. When the student wishes to prosecute biological studies, the mites and a little of the substrata should be removed to the laboratory. Otherwise they may be killed immediately. For rearing work I have used small vials or sections of these mounted on slides and sealed down with gold size. A bit of moist blotting paper with a little suitable food material maintains the mite in a suitable environment and presents an easily studied rearing cage.

Many parasitic species do not leave their host upon the death of the latter and these may be collected from preserved skins in

museums or other repositories. For general field collections a Berlese trap has been found indispensable. The Birge collecting net is very satisfactory for aquatic collecting. Aquatic mites, the Hydrachnidae, have a tremendous vertical distribution, and to secure a representative collection the student must not fail to take this into account.

PHYLOGENETIC POSITION

As

As one reviews the early studies of the Acarina he is at once impressed by the confusion that has existed as to the exact position that the group should occupy in the phylogenetic tree. It has usually been credited with ordinal rank and is so recognized today. Since most of the species are hexapodal during their larval stages they have frequently been grouped with the Insecta. An apparent segmentation of some species has fortified this placement. adults most of them are octopodal and superficially may resemble spiders. Doubt as to the exact ancestry of the group has often led to uncertainty in placing the Acarians. In 1913 Dr. Ewing presented an arrangement of the Acarina dividing them into six quite distinct suborders, and these into eight sections. Altho not the latest scheme to be offered, I shall use it in treating our Ohio mites. A practice which has tended to confuse the relationship of the Acarina in the lay mind and to a certain extent in that of the beginning student is that of thotlessly speaking of some of the more common forms as "insects" or "bugs". The name "lice" is also frequently applied to some of the parasitic forms. Since the entomologist has often been left to deal with both insects and mites it is natural that such a generalization of names should have come into Since the term "mite" is as appropriate for common usage and as easily understood as is that of "insect" or "spider", it should be adopted by biologists to designate the acarina, which are not in any sense insects.

use.

Like the spiders, the body in all the Acarina is divided into two parts, which are usually broadly fused so that in some cases no actual distinction can be made. The anterior part, or cephalothorax, bears the mouthparts, either terminally or ventrally; the anterior pairs of legs; the eyes, when present, and other organs of yet unknown function. The eyes are usually near the lateral margins and occur in one or more pairs which may be either sessile or stalked. There is seldom the median pair of eyes as in the Phalangids.