No. 2303. RED ISPIDERS OF AMERICA— McaUEGOK. 643 



Tragardh (18) veiy fortunately discovered the utility of the collar 

 trachea as a help in the differentiation of the species. In certain 

 species this organ is V-shaped with both arms of equal caliber: in 

 some it is also V-shaped but with one arm much thicker than the 

 other: while in otlier species the collar trachea is straight with a 

 bladder-like enlargement at its end. 



As to any taxonomic importance being attributed to the respective 

 colors of the various species, there is much doubt. Ewing (17) 

 conducted some interesting tests, the results of which indicated that 

 the various shades of green, yellow, orange, brown, and black were 

 attributable to the presence in the blood, tissues, or fecal matter of 

 chlorophyll, or other pigments derived from it through the process 

 of metabolism. The investigations of the present writer (23) of 

 T. himaculatus in South Carolina indicated that the species was 

 subject to much variation in color and that individuals about to 

 enter the wintering existence often became a salmon-yellow color. 

 At various seasons and under varying conditions individuals of the 

 two-spotted mite could be found of nearly all shades exhibited by 

 any species of red spider. It would seem that the color pattern 

 rather than the general color of the species is the important factor. 



Once more it is important to emphasize that the minuteness of 

 the taxonomic structures together wth the aggravating light refrac- 

 tion when emplojdng great magnifications makes the definite con- 

 ception of the microscopic image extraordinarily difficult. This 

 has also been mentioned by a few other workers. 



The red spider body is oval or elliptical, furnished wdth a score 

 or more of dorsal cuticular appendages arranged in four rows. 

 These appendages are usually long and hairlike and either simple 

 or finely plumose, or are in the form of short, rather stout rods. 

 The cephalothorax is separated from the abdomen by a slight 

 constriction, and bears on each side one or two simple eye corneas. 

 The pedipalps are short, the third joint ends dorsally in a strong 

 claw; the last joint is thumblike and bears one or more appendages 

 called "fingers," as well as digituli and sense hairs. In all species 

 examined the palpus of the male bears dorsaUy on the distal margin 

 of the second joint a strong spur. The basal portion of the mandibles 

 are fused to form a broad retractile plate, the apical portion of 

 which is produced into the slender piercing stylet. The legs, the 

 first pair of which are longest, are never much longer than the body, 

 with scattered hairs, the tarsus terminating in claw appendages 

 which vary greatly in arrangement: the name Tetranychus is based 

 upon those species the tarsal claw of which is split into four parts. 

 The anal and genital openings occur ventrally near the tip of th& 

 abdomen; the former is terminal, the latter basal. 



