GALL MITES. 349 



CASE furrowed and striated, more or less, in a transverse direction, 



XVI. 



Tlie Phytopti have the same peciiharity too. Notwithstanding all 

 this, the great stumbling-block (four feet instead of eight) which 

 has choked off the preceding alternatives, would extinguish the 

 idea of connection here also, were it not for the light thrown 

 upon the subject by Von Landois and Low, through the bristles 

 and warts or stumps of feet that they have seen on the underside 

 of the Phytopti. To appreciate the full import of these obser- 

 vations, we must remember that in the Sarcoptidse, especially in 

 those truly parasitic species that live under the skin of other 

 animals, there is a tendency to abbreviate and do away with the 

 organs of locomotion, which shows itself now by contracting the 

 length of the legs, again by the almost entire absorption or 

 atrophy of one or more of the pairs, or by reducing them to the 

 dimensions and form of a wart with a bristle proceeding from it. 

 In Sarcopterus nidulans, all eight legs are contracted to mere 

 eminences, from which spring a number of bristles. In Sarcoptes: 

 scabiei, the female has each of the four anterior feet terminated 

 by a sucker, but there are none to the four posterior feet, instead 

 of which, each is terminated by a stout bristle. The way in 

 which the legs are in these instances contracted, so as to cease 

 to look like anything more than a wart, while still retaining 

 all the parts of a leg, may be seen in the hind legs of many 

 species of Sarcoptes, e.g., in Sarcoptes squamiferus (S. canis of 

 Hering). In Trichodactylus, and in some Hypopi, the pos- 

 terior legs are reduced to a long bristle. Our minds are thus 

 prepared for the substitution ot a wart, with a bristle springing 

 from it for a regular leg ; and when we find that there are four 

 warts with bristles on the underside of the Phytopti, just about 

 where the missing legs should be, one is very apt to accept 

 them as their representatives, without caring very much whether 

 they are only in the shape of a wart and bristle, or the actual 

 *' fusstummel" that Von Landois thought he saw. Professor 

 Westwood suggested that the two long bristles at the tail of 



