68 
ing these organs in a large series of specimens as well as in the various 
species precludes the present possibility of using them for specific 
distinction. I am inclined to believe that there is some variation in 
the form of the vulva, due to the condition of the specimen. The lines 
and ridoes are in a soft tissue, and so are liable to modification and 
distortion. 
There are four pairs of legs in the adult; in the young, as in the 
young of most other mites: but three pairs are present. Each leg 
consists of at least six joints, a coxa, more or less anchylosed to the 
body: a small trochanter; a femur, the longest joint; a patella, about 
one-half the length of the femur; a tibia, slightly longer than the 
patella: a tarsus, longer than the tibia and tapering to a fine point. 
The tarsus, near its tip, has a division more or less distinct, the small 
terminal piece being called the onychium; from the tip of this arises 
the claw, which is usually cleft into four slender parts, whence the 
name of the genus — Tetranychus — four-claw. The first pair of legs is 
the longest, though often scarcely longer than the fourth pair; the 
second and third pairs are plainly shorter than the other two and sub- 
Fiu.4. — Tetranychus: mouth parts, lateral and ventral views— highly magnified (original). 
equal in length. On the ventral surface the basal limits of the coxa 1 
arc not well defined, hut the coxa 1 are rather widely separate. 
The surface of the body is very finely and often regularly striate, 
mostly in a transverse manner. The hairs or bristles are minutely 
serrate, those on the anterior part of body curve forward, those on 
the posterior portion of body bend backward: the long ones on the 
legs appear to stand nearly erect in life, and doubtless have some 
sensory function. 
There appears t<> be much uncertainty regarding the spinning appa- 
ratus, and an examination of a large number of specimens does not 
throw much light on the subject. Dujardin, Pagenstecher. and Don- 
□adieu believed that the thread issued Prom the mouth or in its close 
vicinity. Dufour and Duges asserl that it comes Promtheanal end of 
th< i body. Claparede found some glands opening on the tips di the 
palpi which he considered as silk glands. The thread is not produced 
during the ordinary wanderings of the mitt 4 , but at certain times. 
When mites first attack a leaf there are only a few scattered threads 
lying close to t he Btirface of the leaf, which are attached here and there 
