158 
front margin of the thorax. The trunk is extended near its origin 
and here provided with a thin branch directed backwards. The 
tracheae of the .fourth pair consist of an inner and an outer trunk, 
both bifurcated. 
6. The Musculature. 
Skin Museles. The high development of the cutaneous muscles 
is very interesting, as it has scarcely been observed in any other Acarid ; 
perhaps it corresponds to the segmentation of the abdomen. Each 
muscular band consists of one or mostly of several rather short 
»muscles" going from one group of muscular spots to the other; 
each muscle is composed of one or several strings, extended from 
one muscular spot to the other and consisting of a great number 
of delicate fibres. Almost all the muscles of the abdomen are 
cutaneous, as there are none dorso-ventral muscles as usual among 
the Acari; those of the cephalothorax take their origin from the 
cuticle or the endosternum and go to the appendages. 
The main arrangement of the abdominal muscles is the following 
(pl. V fig. 13). 
From the groove which distinguishes the caput from the thorax, 
a broad band arises on each side which is continued to the anal 
hill (fig. 137). This band, the /ongitudinal interior dørsal band 
becomes more and more narrow posteriorly towards the seventh 
segment, as each muscle here only consists of few strings, but there- 
after it gets broader again and is directed inwards so that the right 
and the left band are almost united to one. In the tenth segment 
the band is fastened to the base of the anal hill and is probably 
used to draw the two anal valves nearer to each other. This 
longitudinal median band is divided into two parts in front, the 
outer and thinner of which is extended into the second thoracical 
and first abdominal segment, while the inner is fastened to the 
groove between the head and the thorax. This arrangement of 
the muscles proves that the two thoracie tergites are to be 
distinguished from the head. The longitudinal exterior dorsal band 
