PEAR LEAF-BLISTER MITES. 85 



rise to the above and to many other forms of gall-growth, and still 

 more their specific description has been (with regard to most of the 

 attacks) a subject of exceeding difficulty. And, further, beyond a very 

 preliminary diagnosis of characteristics, often equally applicable to 

 a large proportion of our most common British Phytopti, we were for 

 the most part without any work to turn to, from which (even with the 

 help of the highest microscopic powers) we might trustworthily identify 

 each species in full. 



We were in the condition described by Dr. Low, the eminent 

 Austrian writer on this subject, when he remarked that even if he 

 were to thoroughly examine the mites out of great numbers of the 

 deformed plant-growths which he had described, still he would not be 

 able to give such sufficient and trustworthy characteristics as would 

 supply the power of specific distinction. 



In fact (to put it shortly), what even the most scientific " Mite- 

 gall " observers needed was something equivalent to a ' Manual,' con- 

 taining fully detailed descriptions of the different species of the " Gall- 

 mites," with measurements, magnified figures, and everything requisite 

 for correct and demonstrably certain identification. 



These now we have in the publications of Dr. Alfred Nalepa, which 

 have been successively issued in the ' Eeports of the Proceedings of 

 the Imperial Academy of Science of Vienna.' During the past summer, 

 Dr. Friedrich Thomas, of Ohrdruf, Gotlia, himself a well-known phyto- 

 pathologist, and observer and writer on Gall-growths, did me the 

 favour to introduce me by letter, relatively to study of Phytopti, to 

 Dr. Nalepa, then Professor in the Eoyal Imperial College, Linz-on- 

 the-Danube, now of the Royal and Imperial Government College, 

 Vienna.''' Dr. Nalepa was good enough to identify for me all the 

 specimens which I sent over, and also to give me valuable instruction 

 as to the anatomical and structural formation of Phytopti, 



In the works of which I give some of the titles appended to this 

 paper, will be found a clear and convenient classification of the family 

 Phytoptidce into subfamilies and genera ; the main distinctions turning 

 on such points as the body being cylindrical, as is commonly the case 

 with the genus Phytoptus, with which we are best acquainted here ; or 

 the abdomen being largest immediately behind the thoracic shield, or 

 other variations of form ; also on the abdomen being similarly ringed 

 throughout, or with the rings broader on the back and narrower below, 

 or other variations. 



With the kind permission of Dr. Nalepa, I have given a copy of 

 one of his very numerous and clearly drawn illustrations at the heading 



* Prof, an der K. K. Lehrer-Bildungsanatalt, Linz-U'Donau, Austria ; now of 

 K. K. Staats-gymnasium, Vienna. 



