THE ACAEIXA OR MITES. 



13 



rebuilt from the disintegrated tissues of the preceding stage. The genital organs are, 

 however, not affected by these histolytic processes. 



Renter has recently (1909) tabulated the known life histories of mites, showing that 

 most species have three nymphal stages. In several cases the second stage is absent 

 or has not been observed; in most of the sarcoptid mites there are but two nymphal 

 stages, while in the Eriophyidae and Ixodidae there is but one nymphal stage. 



Various authors have expressed their belief in parthenogenesis in Acari, but without 

 experimentation. Miss Foa and Dr. Oudemans have examined most of the alleged 

 cases and show that there is no direct evidence, or that there has been a mixture of 

 species, as in Trouessart's theory of the parthenogenesis of Syringohia. It was also 

 held that Syringophilus was a par- 

 thenogenetic form of Cheyletus 

 norneri; Dr. Oudemans has shown 

 that this is erroneous, and Norner 

 described the males of Syringophi- 

 lus. The cases given by Berlese 

 in the Parasitidae were examined 

 by ^liss Foa, who concluded that 

 there was no proof, for at the 

 proper season the male of each spe- 

 cies appeared, although in some 

 species they live but a brief time. 

 There is, therefore, no positive proof 

 of parthenogenesis in acarians un- 

 less recent claims for parthenogene- 

 sis in a tick should prove to be true. 



The common impression that 

 most mites are parasitic is entirely 

 erroneous. About half of the known 

 species are not parasitic in any 

 stage, and many which are found 



attached to insects and other animals are not true parasites thereon. The relation 

 between the host and the parasitic acarian is of such a varied nature that several 

 writers have made elaborate classifications of their relationships. But, as with most 

 classifications, there are intermediate forms. 



It is evident that the parasitic habit has originated independently a number of 

 times in mites, since in several families of mostly free-living forms there are parasitic 

 genera. Also there Is a different method of origin of parasitism in the different cases. 

 Many free-living parasitids occur in nests of small mammals, finding there an abun- 

 dance of food in the decaying matter, or small insects; so it is not strange that some 

 parasitids {Laelaps, etc.) feed on the animal itself. Other parasitids have the habit 

 of using various insects as a means of transportation from one breeding place to another 

 suitable locality. Some of these mites, finding on the carriers an attractive food, 

 have started a line of forms parasitic on insects. 



Certain species of Tyroglyphidse occurring on the bark of trees have had the oppor- 

 tunity to attack scale insects, and so developed genera usually predaceous on scale 

 insects or their eggs. The ladybird beetles, being numerous about scale insects, were 

 utiUzed by the mites for transportation; thus some of these mites, finding the lady- 

 bird beetles a suitable food, originated another group (Canestrinio) , parasitic on these 

 and other beetles. Some species are very restricted in the matter of hosts; others will 

 attack almost anything. Those forms that attach by their beaks to suck blood are 

 general feeders; those that have some specialized apparatus of legs or palpi to hold to 

 their host can have but little range in host. Thus few ticks are confined to any one 

 kind of animal, and frequently the young are found on a different host than that 

 attacked by the imago. Many of the red bugs will attack any living thing, but on 



Fig. 



A mite, Trombidium: Egg, larva, and adult, 

 (Original.) 



