NO. II LEGS OF PRIMITIVE ARTHROPODS EWING 7 



be added incidentally that they are the only two individuals ever taken 

 in the New World. Under these conditions it has been impossible to 

 study the muscles, hence the following homology, that is given only 

 as a suggestion, is based on a comparison of the Holosiro leg with 

 that of a solpugid and of a primitive mite genus, both of which have 

 the same number of segments. 



The basal segment, the so-called maxillary lobe, is probably the 

 subcoxa, the next is a large coxa, flattened so as to be platelike at 

 the base, then follows the first trochanter, a short segment, pedicellate 

 in the first two pairs of legs. The next segment is the longest of 

 all and in size and position suggests the femur. A comparison, how- 

 ever, with the leg of the related primitive mite genus Labidostontnia. 

 the musculature of which was worked out, shows that this long seg- 

 ment probably represents the second trochanter. The fifth segment 

 is short in the first legs but is one of the longer segments in leg IV. 

 It should be regarded as the femur. It is a more important segment 

 than the femur of Labidosfoiimia (pi. 2, fig. 3). There follow three 

 somewhat similar segments, the last bearing a single claw. These 

 should be regarded as the patella, tibia and tarsus respectively. The 

 homologizing of the leg segments of Holosiro with those of the more 

 highly developed phalangids is not attempted. 



THE LEG SEGMENTS IN SOME OF THE ACARINA 



Probably the most nearly related to the generalized phalangids of 

 all the mites, and hence the most primitive, are those placed in the 

 rare and little studied genus Lahidostoinina. The writer is fortunate 

 in possessing a numljer of mites of this group representing several 

 species. 



In recently transformed adults with a thin coat of chitin the muscle 

 attachments may be made out without difficulty. In the front leg 

 of Lahidost omnia (pi. 2, fig. 3) there is a broad basal platelike seg- 

 ment with hinged articulations for the second short, stout segment. 

 The latter bears a pair of hinged articulations for the third reduced 

 segment. The third small segment is immovably joined to the fourth, 

 which is femurlike and the largest of all. Then follows a short 

 movable segment, two long movable ones and a long terminal claw- 

 bearing segment. If the basal, platelike segment be regarded as the 

 subcoxa, then there follow a rather small but fairly typical arachnid 

 coxa, a very large divided trochanter, a reduced femur and another 

 segment which is here regarded as the patella, and lastly the tibia 

 and claw-bearing tarsus. 



