482 



NA TURE 



[March 2;, 1902 



reviewer ventures to suggest that better materials exist 

 than such scraps of science which form the pabulum of 

 the average science master, and are reproduced in 

 wearisome iteration in the scores of elementary text- 

 books which it appears to pay our publishers to bring 

 out ; if the latter, it must be confessed that our (jerman 

 neighbours, who have not as yet adopted such methods, 

 are more prolific in quantity of research, at least, than 

 we. VV. R. 



CHEESE-MITES. 

 British Tyroglyphidae. By Albert D. Michael, F.L.S., 



F.Z.S., F.R.M.S., &c. Vol. i. (London : Printed for 



the Ray Society, 1901.) 

 T F the world sometimes knows little of its greatest 

 men, it often knows still less of its most familiar 

 fellow-creatures. To work out the story of a cheese- 

 mite with proper completeness is a task which many 

 might undertake in a spirit of condescension, only to 

 retire from it helplessly disconcerted. Vet none need be 

 deterred from the enterprise by want of specimens, for 

 though the Tyroglyphida; are but one family out of many 

 in the host of the Acarina, they produce a population 

 absolutely beyond estimate in numbers. Together with 

 the few species which, in accordance with the family 

 name, are really " sculptors of cheese," there are many 

 others that use a quite different diet. On learning that 

 they like senna as well as dried figs, cantharides as well 

 as French plums, that they are partial to decaying mush- 

 rooms, that they eat hay with equine avidity and dote on 

 rush-bottom chairs, the reader will infer that they have a 

 fine catholicity of taste in which our prejudiced palates 

 can only partially follow them. The ubiquity of these 

 minute animals betrayed one experimentalist into believ- 

 ing that he had been able to create them by electricity. 

 From such points of general interest with which Mr. 

 Michael enlivens his introductory chapter, he proceeds 

 to aspects of his subject which have a fascination for many 

 who care nothing for the subject itself. There is seldom a 

 group of animals, however low in popular esteem, that 

 does not occupy a considerable space in the literature of 

 ■science. Still more rarely, perhaps, has any group 

 escaped all erratic movements in the course of classifica- 

 tion. A clear-sighted guide, himself in the forefront of 

 existing knowledge, renders first-rate service to scientific 

 progress in general when for his special branch he shows 

 how the explorers have opened the road for their suc- 

 cessors or how they have obstructed it. The path of 

 investigation is ever liable to be deflected, arrested or 

 reverted by the failures of the infallible, the specious 

 finality of those who attempt to do too much, and the 

 slovenly ineffectiveness of those who are content to do 

 too little. Notwithstanding the invariable courtesy with 

 which Mr. Michael writes of his predecessors and 

 fellow-workers, one may perceive from the bibliographical 

 survey here, as well as from that in his earlier work on 

 the British OribatidiL', that the study of mites has not 

 been wholly free from "regrettable incidents." Immor- 

 tality at any price seems to be the watchword of those 

 who describe species in such a fashion that no succeeding 

 naturalist can make out what animals precisely were 

 intended by the descriptions. In discussing the common 

 NO. 1691, VOL. 65] 



properties of a group and the broad lines of its classifi- 

 cation, less harm is done by the careless and the muddle- 

 headed, because their mistakes in these departments can 

 eventually be corrected, and as when thieves fall out 

 honest men come by their own, so sometimes from a 

 conflict of errors truth finds a chance of emerging. 



In the ordinary doctrine of text-books the Acarina are 

 distinguished from other arachnids as having, not only 

 the head and thorax coalesced, but the cephalothorax 

 itself completely fused with the abdomen. In the pre- 

 sent volume, however, it is pointed out that there is very 

 frequently found a constriction or furrowing of the body 

 Jaehind the second pair of legs. This is held to justify 

 the application of the term abdomen to the part of the 

 organism behind the constriction or furrow. But such 

 an allotment of the first two pairs of legs to the cephalo- 

 thorax and of the last two pairs to the abdomen would 

 surely be equivalent to severing the Acarina from the 

 arachnids altogether. From segmental demarcation 

 between the second pair of legs and the third nothing 

 more can properly be inferred than that one part of the 

 thorax is more intimately fused with the head and the 

 other part with the abdomen. It is quite true, as Mr. 

 Michael argues, that the Malacostraca are abundantly 

 supplied with abdominal limbs, but these are always 

 sharply distinguished in character from the thoracic 

 appendages, unless in some unique monstrosity. In the 

 case of the Acarina, no perceptible advantage is gained 

 by a theoretical transfer of limbs from the thorax, on 

 which they are normal, to the abdomen, where they 

 would be anomalous. 



On other subjects Mr. Michael is much more con- 

 vincing. His whole discussion of the acarine " nymph" 

 is highly interesting and worthy of admiration. While 

 the larva perhaps never, and certainly hardly ever, has 

 more than six legs, the nymph like the imago or adult 

 has normally eight. The nymphal stage extends from 

 the acquisition of the full number of legs to the last 

 exuviation. There is, however, one group in which it is 

 still uncertain " whether the nubile female is a nymph or 

 an adult." Here the difficulties of investigation are very 

 great, the little creatures being found usually in numbers 

 on the feathers of birds, and, as they will not live away 

 from the host, the isolation necessary for observing the 

 whole series of their transformations seems practically 

 impossible to arrange. Nevertheless, the account given 

 of the genera Ilypopus and Homopus shows how diffi- 

 culties can be made to yield to untiring patience, such as 

 both Mr. and Mrs. Michael evidently combine with other 

 valuable accomplishments. Opinions upon the supposed 

 genera just mentioned have been various and fluctuating. 

 The final result is to establish clearly that the two names 

 in question are not of generic value. They simply refer 

 to a particular stage in the life-history of the Tyrogly- 

 phidit. For designating this stage they are still valid, 

 although they do not add to the musical charm of a 

 sentence by making us speak of hypopial nymphs and 

 homopial hypopi. The difference is concisely expressed 

 by the statement that the hypopus is homopial when " it 

 adheres to its temporary host, not by suckers, but by 

 holding one or more of the hairs of tlie host between 

 special plates on the ventral surface of the parasite." 

 Suckers facilitate adherence to smooth chitinous insects 



