286 ME. A. D. MICHAEL ON THE VAEIATIONS IN THE 



many disappointments. The result, however, has been the gaining of considerable 

 information on the point, and I think the process observed is sufficiently curious to make 

 it by no means the least important part of this paper ; it is, I believe, totally unrecorded 

 except so far as some portions of it are treated of in my own notice, referred to below, of 

 Gamasiis terribilis, when I discovered that species, which was the first upon which I 

 made observations that have indiiced mo to follow out the subject. 



Finally, there are unrecorded facts tending to prove that in some cases the internal 

 organs are important in the classification of the Gamasidse by showing relations between 

 subfamilies or genera not previously understood. 



Of course it is in the highest degree improbable that in the limited number of species 

 to which my attention has been turned I have found more than a small proportion of the 

 variations existing in this large family of Acarina ; doubtless niimerous others remain to 

 reward future research. 



Modes of Investigation. 



The methods which I have employed in the present inquiry have been three, viz. 

 1. Dissection ; 2. Serial sections ; 3. Observation of the living creature. Of these 

 methods actual dissection has been chiefly employed ; I have endeavoured, as far as 

 possible, to confine myself to species where I could obtain an ample sujoply of specimens; 

 and although I could not altogether succeed without neglecting many interesting cases, 

 yet it has been the rule ; and where I have had a sufficient supply I have not confined 

 myself to a few dissections, but have repeated them over and over again, until I had 

 either thoroughly satisfied myself upon the points in question, or else found it impossible 

 to carry the inquiry further by this means. I have not ever relied upon a single 

 dissection. All the figures of whole organs in the Plates illustrating this paper have 

 been drawn from such dissections. 



I have found that with these delicate and minute creatures I have not been able to 

 dissect specimens which have been treated with hardening agents such as alcohol or 

 picric acid, or any other of the well-known reagents, as successfully as fresh specimens ; 

 I have therefore usually dissected them immediately after death. I at first employed 

 boiling water to kill with, but have subsequently abandoned it in favour of the fumes 

 of chloroform, when the specimen was intended for dissection. Staining has been done 

 either after or during dissection. All dissections have been done by the aid of Stephenson 

 binocular microscopes. 



Serial sections, sagittal, horizontal, and transverse, of each species have been em- 

 ployed, both to check the dissections and to trace out points not ascertainable by dis- 

 section; here again I have endeavoured, in each instance, to have several series of 

 sections of each species in each direction. The sections have been chiefly cut with a 

 Cambridge rocking microtome. The creatures used for the purpose were either killed in 

 the same manner as those for dissection, or else l)y boiling after Prof. Lowne's method to 

 solidify the blood-plasma around the organs ; some were then treated with dilute picro- 

 sulphuric acid, and subsequently passed through alcohol, of gradually increased strength 



