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THE ORIGIN AND DEVELOPMENT OF PARASITISM AMONG THE 
SARCOPTIDZ.* 
By H. GARMAN, Lexington, Ky. 
Assuming the evolution of species through the action of natural selec- 
tion as established, we are at once met, in considering the origin and 
development of the parasitic habit in Sarcoptide, with the ques- 
tions, what were the originals of the family and did it diverge from 
the non-parasitic mites before or after the order Acarina became es- 
tablished? In other words, were the originals of the Sarcoptidz mites 
or were they something else? A more intimate knowledge of the forms 
we are considering will doubtless give us better ground than we now. 
have for conclusions on the subject. In the light of present knowledge 
it seems altogether probable that the immediate ancestors of the Sar- 
coptide were not only mites, but that they differed little, if at all, 
from species now in existence. 
Tn deciding the position of an animal among its fellows we are prone to 
be influenced by the idea of our own supremacy, and to rate it by its 
complexity of structure or by its intelligence as shown by habit. Sys- 
tematists sometimes lose sight of the fact that evolution does not al- 
ways mean an increase of structural perfection, but often of the reverse 
process, a simplification and reduction. The simplicity due to degener- 
ation from one cause or another is liable to be mistaken for the simplic- 
ity of lack of differentiation; and parasitic and other animals whose 
parts have been reduced from disuse have sometimes been placed at 
the beginning of a series, when their proper place, it may be, is at the 
end. 
The Acarina seem to mea group of these degraded animals, and 
their place, if this is true, is not at the beginning of the line of Arach- 
nidan descent. I subscribe to Gegenbaur’s remark (Comparative An- 
atomy, English translation, 230, 1878): : 
There seems to be no doubt that degeneration is present in these, and is indicated 
by the parasitism which obtains in most of the families. 
Reasons for considering the Acarina degraded Arachnids apply with 
the same force to the Sarcoptide among Acarina. The fact that they 
are parasitic and at the same time diverge but little from the free-living 
mites is good evidence that they are not the stem upon which the order 
has developed. The further fact that they are parasitic only upon mam- 
mals and birds speaks for their being a family of recent appearance. 
The geological history speaks to the same purpose of the order. 
This view of the position of the Acarina among Arachnida, and of 
‘the Sarcoptide among Acarina, calls for some notice of several aberrant 
animals which are commonly placed with the Acarina, and frequently 
in or near the Sarcoptide, because of a supposed relationship between 
the Sarcoptide and the Vermes. 
* Read before Section F, A. A. A.S., at the Washington meeting, August, 1891. 
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