190 The Phytoptus of the Vine. By Prof. Giovanni Briosi. 
itself, with the outlines of the head already sketched and distinct, 
and with the traces of the rings on the body (Fig. 9). In Fig. 10 
an animal is represented which scarcely left the vitelline mem- 
brane a, to which it is still adhering (attached). In this stage no 
hair could be seen as yet, neither were the legs all formed. 
The smallest animals I found measured 0°045 mm., and there 
I saw already the posterior dorsal hairs (which seem to be formed 
first) and the small cylinders of the ¢ars¢. The largest animals I 
found reached 0:1513 mm. in length, and between these two limits 
I found every size. 
I have said that this mite (acarus) has four legs only. 
Landois, however, found under these well-developed legs, two 
other rudimentary pairs. He relates that these acari, before 
they have reached their complete development and are fit to 
generate, pass through at least four changes: the first taking place 
when they leave the egg and get the tarsus projections; in the 
second they become simply larger; in the third they get the first 
pair, and in the fourth the second pair of rudimentary legs. Thus, 
he adds, the general rule, that all the acarzi when fully developed 
possess four pairs of legs, is fully confirmed.* I believe that 
Landois is mistaken; the four rudimentary legs, represented by 
four small appendixes, each terminating with a bristle, I have 
been unable to perceive. ‘There are, it is true, sometimes found 
animals who might easily give rise to such an idea, because on the 
spot where he puts the rudimentary legs there is an elevation 
terminating in a bristle; but under close observation one sees 
that this is due to the genital valve, which is found more or less 
raised by the action of the body under it, which seems to prepare 
itself for the expulsion of eggs. ‘Thus the bristles do not form part 
of the raised appendixes, but are attached to the hairs of the body, 
nearly at the margin of the genital aperture, as seen in Figs. 2 
and 3, from which I conclude that these animals do really constitute 
a special genus of acart, which have only four legs. 
These arachnida seem to possess a most extraordinary tenacity 
of life. Sorauer saw them moving the legs after being twenty, and 
Landois after twenty-four hours in glycerine.t From the fact of 
their being able to live so long in a liquid like glycerine, Landois 
argues that their respiration is neither pulmonary nor tracheal, 
that it cannot even be cutaneous, and concludes that they must 
breathe through the anal opening. 
These acart are found on the vine at whatever season of the 
year it is examined, and Landois is in error when he affirms that 
they all die at the first diminution of temperature, that the eggs 
only remain between the hairs of the leaves, which fall in autumn, 
* Kine Milbe als Urs. d. Traubenmiss, p. 357. 
+ Frauendorfer Blatter, 1873, No. 30. (Sorauer.) 
