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J. R. AUDY 
one stage of the life-cycle but differently, or hardly at all, in the other : in an example from the 
Anopheles umbrosus group, Reid (1950:315) has remarked that it “ looks as if the evolution of 
larval and adult characters in some of these species has proceeded independently along some- 
what divergent lines.” This is to be expected when the larval and post-larval stages lead such 
very different lives. Adaptive and other modifications involving the larvae cannot be expected 
to be reflected by corresponding modifications in the post-larval stages, and vice versa. Our 
main interest in trombiculid mites at present is in their behaviour as parasitic larvae, and it 
would probably be rational to give more weight to a larval system of classification whenever 
this is seriously at variance with a post-larval system. Compromises may readily lead to serious 
difficulties. There is no doubt that taxonomic revisions of the trombiculids should be made 
very cautiously and not be based on local studies, at this stage, however meticulous these may be. 
2. Standard measurements of Nymphs/ Adults. — The use of the following measurements in 
the descriptions of nymphs and adults has been agreed upon jointly by Dr. Douglas Gould and 
the present writer, based on the work done by Jenkins (1949), Wharton et al. (1951), Womersley 
(1952, and various papers), and Wharton & Fuller (1952). The measurements and their 
abbreviations are offered provisionally pending the publication of joint papers in the next 
Study in this series. The suggestions made below will doubtless be elaborated during the 
completion of these papers. In describing nymphs and adults the worker confronted by a 
badly mounted or faded specimen must be borne constantly in mind. Points from which 
measurements are made should be clearly discernible (e.g.,the exact ends of the crista cannot 
be accurately decided especially in old specimens, hence its length will vary greatly when 
measured by different workers). Ratios are generally of much greater value than arrays of 
measurements. A method of graphic or tabular presentation (as with Standard Measurements 
of larvae) is being devised, and the abbreviations are proposed with this in mind. 
Suggested Standard Measurements (Fig. 1) — 
Body : Length and Width of propodosoma. 
Gnathosome: Lengths of femoral and tibial setae 
Lengths of Claw and Tibia (ratio claw/ tibia) 
Length of cheliceral blade 
PRelative proportions of palpal segments. 
Scutum: Cristo-tectal length (CTL) from where crista expands into saddle to first median tectal 
setal base. 
ASL — anterior scutal length 
SB — sensillary bases Ratio ASL/SB 
C — crista 
K — length of carina, when present 
PSL — posterior scutal distance 
PAD — posterior apodeme 
E/ED — diameter of eye/interocular distance 
TS — tectal (epistomal) seta(e) 
SS — parascutal setae 
SENS — sensilla 
Legs : proportional lengths entire legs when possible 
Length/Height, Tarsus I (and L/ Width, as height may not be measurable in many) 
Lengths, Tarsus I/Tibia I 
Lengths, Tarsus II/Tibia II 
Genitalia: ?Ratio of axial lengths anterior and posterior suckers in nymphs 
Ratio of axial lengths genitalia to anus. 
Body Setae : lengths and wherever possible ratios of lengths of anterior dorsal setae, posterior dorsal 
setae, and ventral setae. 
3. Chaetotaxy of legs , Nymphs /Adults. — The leg setae have been almost completely 
ignored because they rapidly become difficult to study in old mounts and because they occur in 
dense setal forests which would deter the most enthusiastic worker. It is however necessary 
to explore these setae for their possible taxonomic importance, and the present writer has found 
that the forests of setae can be reduced to some sort of order without undue effort. 
STUD. INST. MED. RES. 
