NATURE 



141 



THURSDAY, JUNE 12, 1884 



BRITISH MITES 



The British Oribatida. By A. D. Michael. (Ray Society, 

 1884.) 



WE congratulate the Ray Society on this valuable 

 addition to their excellent series of monographs. 

 Mr. Michael indeed modestly asks us to " kindly remem- 

 ber that this book is the record of work done in the 

 scanty leisure of a very busy man," but though this may 

 add to our gratitude, and serve as an encouragement to 

 others, no one, we think, after reading the book will feel 

 that any excuse or apology was needed. When Mr. 

 Michael commenced his study of this curious family of 

 mites scarcely any species were recorded as British, there 

 were very few of which the whole life-history was known, 

 and Nicolet's was the only work dealing with the anatomy 

 of the family. 



Mites are not perhaps a very attractive group, neverthe- 

 less many species are extremely curious and some very 

 pretty, as a glance at Mr. Michael's excellent figures is 

 sufficient to show, especially those of Tegcocrantts latus, 

 Leiosoma palmicinctum, and Cepheus ocellatus j possibly 

 indeed, says Mr. Michael, " no more bizarre or remark- 

 able creatures exist than these, when nearly fully grown, 

 and bearing on their backs, ring within ring, concentric 

 circles or ovals of these curious and disproportionately 

 large line-of-beauty shaped spines formed of clear, colour- 

 less chitin, and strongly serrated in the first species, and 

 of the beautiful and iridescent membranous fans in the 

 two latter." 



Some, he adds, especially " of the immature stages are 

 amongst the most beautiful, creatures of the order; and only 

 those who are not acquainted with the Acarina can suppose 

 that none are beautiful. It is needless to say that the Ori- 

 batidae are highly interesting and instructive, because the 

 same thing may be said of every family of created beings ; 

 no one can devote himself to the study of any class of 

 organism without becoming from day to day more deeply- 

 impressed with the admirable manner in which its mem- 

 bers are adapted to their wants, and the marvellous way 

 in which the different parts are varied in different species, 

 so as to provide more efficiently for their protection and 

 continuance. This fact of having constantly before his 

 eyes the wonders of the individual family or order which 

 he is investigating is apt to cause the specialist to forget 

 for the time that there are hundreds of other families 

 equally interesting, beautiful, and wonderful in their con- 

 struction and life-histories. It is only by endeavouring to 

 base his special knowledge upon the wider foundation of 

 general interest in the works of nature that the naturalist 

 escapes this error, and appreciates the harmony between 

 the particular class and other equally glorious types of 

 life. Endeavouring to bear all this in mind, I feel that I 

 am not justified in saying that the Oribatidas have any 

 claim on the biologist beyond that of any of the endless 

 varieties of other forms of animals ; but I do say that they 

 hare an equal claim ; and I think I may confidently assert 

 that any observer who inquires into the complex structure 

 Vol. xxx. — No. 763 



of these minute creatures, their singular life-histories, or 

 the quaint and somewhat exceptional habits of some of 

 the species, will rise from his task fully rewarded for the 

 time that he has spent." 



The work is divided into two parts : in the first the 

 author gives an account of the terminology, literature, 

 classification, development, habits, methods of collection 

 and preparation, and anatomy ; while the second is 

 devoted to descriptions of the genera and species. 



The principal home of the Oribatidse is in moss of 

 various sorts, on lichens, and in fungi ; others live in dead 

 wood, many are found in the debris under furze bushes, in 

 the needles of which the nymphs burrow. Pelops, Hoplo- 

 phora, and others are found among the fallen leaves of 

 Scotch pines ; some frequent other trees, while Oribata 

 sphagni and Notaspis lacustris are aquatic. The whole 

 family with one doubtful exception are vegetable feeders ; 

 and, being without any weapons of offence, are all the more 

 in need of defensive arrangements, with which indeed they 

 are liberally provided. Their carapace is thick, with in 

 many cases curious provisions for the protection of the 

 legs, and they most of them have the habit of shamming 

 dead. 



Mr. Michael differs from the account given by Nicolet 

 of the internal anatomy in several important respects, and 

 considers that the conspicuous organs, usually called 

 stigmata, are really organs of sense, probably of hearing 

 or smell, and he says, " I incline to the former." 



The life-history falls into four well-marked periods — the 

 egg, larva, nymph, and imago. Dujardin indeed asserted 

 that the Oribatidas are viviparous, and the statement has 

 been repeated in various standard books, but as a general 

 rule the reverse is the case. The egg is generally ellip- 

 tical, or cylindrical with rounded ends. In some cases it 

 absorbs moisture, and the exterior membrane, being hard 

 and brittle, splits longitudinally and allows the inner or 

 vitelline membrane to be seen through the opening. 

 This constitutes the stage called by Claparede the 

 " Deutovum." 



The larva is invariably hexapod, and all six legs are 

 monodactyle, tridactyle tarsi being confined to the imagos. 

 The larval stage is comparatively short, generally lasting 

 from three weeks to two or three months. Mr. Michael 

 does not consider that the larva undergoes any change of 

 skin until it passes into the nymph. 



The nymph " may be defined as the creature after it 

 has become octopod," but before the first month. It is 

 the principal period of growth and occupies a consider- 

 able proportion of the lifetime ; " it is also the time of 

 gay colouring and of beauty." " When the nymph is 

 fully fed, and is about to become an imago, it creeps into 

 a hole, or some other sheltered position, stretches out its 

 legs, fixing its large monodactyle claws firmly into the 

 substance it is resting on, and then gradually becomes 

 inert, perfectly motionless, and to all appearance dead ; it 

 ceases to feed, and does not exhibit any sign of life if 

 touched or injured." 



Mr. Michael coincides with the opinion of Claparede 

 and Me'gnin that during this period there is an entire re- 

 organisation of the internal structures, and " the different 

 parts of the body of the adult are formed, not at the 

 expense of the same parts of the nymphs, but from the 

 general body substance." 



