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. fioricolus and 

 T. hominis, 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. tvoodi 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. hom,inis, 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. woodi the fourth pair 

 is not 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. woodi. 



