G. H. F. Nutt all 
o 
remains of pattern either disappear or but traces remain in certain regions 
perhaps partly because these are less accessible to contact with the caustic. 
On the other hand, where the scutum is dark brown or black, as in certain 
thicker and well-defined portions where ‘"dark markings'' are referred to in 
descriptions, these markings persist after caustic treatment. It is interesting 
to note that the bright orange spot occupying the centre of the scutum in 
Amblyomma splendidum £ (illustrated by me in Parasitology , vi. PI. VII, 
figs. 5 and 6) appears to offer an exception in that it corresponds to a dark 
spot in caustic-treated specimens, whilst no similarly situated dark spot is 
observable in the scutums of the closely allied species A. hebraeum, A. 
cohaerens, etc. 
SUMMARY AND CONCLUSIONS. 
The coloration of Amblyomma hebraeum , A. gemma , Dermacentor venustus, 
D. variabilis and D. reticulatus niveus, as seen in living examples, is depicted 
for the first time, and the desirability of recording the colours of ornate ticks 
when alive is indicated. 
A remarkable change in colour in living specimens of A. hebraeum is de¬ 
scribed and figured, this change taking place after a prolonged sojourn (74- 
141 days) upon the host. Such a colour change has not hitherto been observed 
in ticks. The difference in colour is seen in dead dried specimens but is not 
appreciable in those preserved in alcohol. 
Since the immature stages of ornate ticks are inornate, and the colours 
change in adults of some species during prolonged periods of parasitism, it is 
evident that the coloration in adults must depend upon the accumulated 
products of metabolism beneath the chitinous exoskeleton, the regional dis¬ 
tribution of colour depending upon special metabolic functions taking place 
in corresponding parts of the tick. The ornamental colour-producing layer 
can be scraped away from the underside of the scutum in most ornate ticks 
and it is removable from such ticks by the use of caustic potash. 
The whitish or creamy coloration that is so characteristic of most species 
of Dermacentor and the three ornate species of Rhipicephalus that are known to 
science, appears on the other hand to depend largely upon inclusions or 
structural changes within the chitin itself, whence the persistence of the creami¬ 
ness seen by reflected light in the caustic-treated ticks. Similar, but less 
distinct, appearances may be seen in ticks belonging to other genera. Derma¬ 
centor rhinocerotis, which does not exhibit creamy coloration but only dull 
yellowish spots when dry, is totally decolorized by caustic potash, whilst 
contrary to most species of its genus it shows metallic coloration in well- 
preserved specimens in alcohol. 
The examination of caustic-treated specimens was carried out upon 31 
species of ornate ticks, i.e. Dermacentor (8), Rhipicephalus (3), Amblyomma (15), 
Aponomma (4) and Hyalomma (1 species). 
The coloration and creamy ornamentation, herein distinguished, appear 
