ISLE OF WIGHT DISEASE IN HIVE BEES— ACARINE DISEASE. 
775 
male is relatively large and of robust build, and terminates in a stout curved spine. 
These features are regarded as of value in mating. In the male of T. hominis this 
limb appears definitely smaller in size and general build in proportion to the other 
parts as compared with other species. Dahl interprets this as related to an endo- 
parasitic life. In view, however, of our very slight knowledge of this species, and 
especially on account of the doubt which exists as to its normal habitat, the 
conclusion must be received with reserve. 
If we apply such a comparison to T. muris and T. equi (T. sauli Dahl), these 
occupy an intermediate position between such a species, e.g., as T. jloricolus and 
T. ■ liominis , and so far affords some support to Dahl’s view. 
Including T. woodi in this comparison, we regard its place as undoubtedly at the 
end of the series. T. woodi agrees with T. hominis in general appearance in both 
sexes, but in detail more closely in the male than in the female. In the male they 
agree in possessing on the second pair of legs a sensory organ (riech-haar of 
Oudemans) of relatively large size as compared to the one on the first pair. The 
reduction in size of the last pair of legs is also a common feature, although in 
T. woodi the whole limb is markedly slighter in build than in T. hominis. With 
respect to the terminal claw also the comparison is interesting. In T. hominis , though 
showing the inward curvature characteristic of the genus, this is smaller than is the 
case in all the hitherto known species. In T. woodi the limb appears to terminate 
in a straight, sharp spine. The mite has been seen carrying this spine directed 
inwards at right angles to the limb. Under a high power it exhibits an appearance 
similar to that of the sensory organ upon the anterior limbs, and there is doubt 
as to its homology with the terminal claw present in other species. Whatever view 
we take regarding the reality of the endoparasitism in T. hominis , etc., I incline 
strongly to the view that these special features in T. woodi are to be interpreted 
in relation to the fact that the habitat of the male is probably limited to the 
tracheae of the host, and also that mating takes place in this confined space. These 
conditions largely obviate the necessity for specialised clasping limbs. At the 
same time a sensory organ on the limb would obviously be of value. 
Another feature worthy of notice is found in the nature of the ventral surface, 
which is devoid of the five longitudinal epimeral grooves which are prominent in 
most species, including some of those which are regarded as endoparasitic in 
mammalia, e.g. T. hominis. 
In the female of T. woodi fewer points of comparison can be laid hold of. The 
most noteworthy are to be observed in the two hinder pairs of legs. These in 
T. hominis and in T. sauli are comparatively weak and slender. In both cases the 
fourth pair terminates in the usual two long bristles. In T. ivoodi the fourth pair 
is hot slender, but is reduced to three segments, is somewhat stumpy, and its two 
bristles are long and sweeping. Pseudostigmata have not been described in any 
of the so-called endoparasitic species, and they have not been observed in T. ivoodi. 
