210 DR JOHN RENNIE ON 



species. The external genitalia consist of two rounded lobes, projecting posteriorly 

 on each side of a tapering triangular penial sheath. 



Legs. — Special features regarding the limbs are : On the penultimate segment 

 of the second pair of legs there is a prominent sensory organ. The fourth pair of 

 legs is relatively slender, and presents the most distinctive characteristic of the 

 species in this sex. There are three joints, all of which are comparatively weak ; 

 the terminal one bears the very long, stout, and finely curved hair distinctive of 

 the genus. Just within this, and almost at the tip of the last segment, is a small 

 straight spine, which occupies the position of the incurved terminal claw, charac- 

 teristic of free-living species. Close examination has suggested that this structure 

 is of the same character as that on the second pair of legs of the males, and on the 

 female limbs also, and that it is probably sensory in function (fig. 7). 



Larva. — The larva is large, being about '2 mm. in length by about "08 mm. in 

 width at its broadest part. The mouth parts resemble those of the later stages. 

 There are three pairs of short legs ; the first terminates in a double claw (fig. 4). 



Ovum. — The egg is large, being about "14 mm. long by "06 mm. broad, and 

 slightly concave along one side (fig. 2). 



All the Heterostigmata appear to be parasitic, some on plants, others upon 

 insects, and doubtfully on warm-blooded vertebrates. The majority of the described 

 species of Tarsonemus are found upon plants ; the others are from the bodies of 

 vertebrate animals, in which a number have been found associated with malignant 

 growths. T. woodi, n. sp., appears to be the only species known to ^occur in 

 insects. Its discovery as an endoparasite within the hive bee therefore constitutes 

 a significant advance in our knowledge of these mites, and of the general importance 

 of the genus, apart from the far-reaching suggestiveness of its causal relationship 

 to a disease in hive bees which has baffled inquiry for the last sixteen years. 



As giving a more detailed indication of the habits of the genus, the following 

 brief references to the best-known species are submitted. In view of the importance 

 of habit and habitat in the case of T. woodi, I have preferred to refer to these, 

 not in the order of their original discovery or description, but to group them 

 from this point of view. 



Gall-forming Species. 



T. jloricolus On. and F., 1876. — This species is described as occurring on the 

 flowers of Verbascum, forming galls in foliage of Vitis vinifera, Coryllus avellana, 

 Salix alba, etc, in putrefying stuff, and in frass of bacon beetle. T. (Cheylurus) 

 socialis, according to Berlesk, is of the same species. It is described from the skin 

 and base of the feathers of birds of very diverse species, both terrestrial and aquatic. 



T. buxi Canestr. and B., 1884. — Occurs as an inquiline in Fhytoptus galls and in 

 Diplosis galls. See Canestrini (1886), pp. 320-1, 



