444 R. I. POCooK. 



terguni of the first leg-bearing somite; in the ankylosis of 

 the second and third segments of the legs of the last pair; in 

 the incipient differentiation of the metameres into alternating 

 major and minor leg-bearing somites^ the regularity of the 

 alternation^ however, being interrupted at the seventh and 

 eighth somites, both of which belong to the major category; 

 in the power to withdraw the anal and genital somites out of 

 harm's way into the last leg-bearing somite, in the total dis- 

 appearance of the female gonopods, and the reduction of the 

 segments of the male gonopods to one. With the shorteniug 

 of the body and the lessening of the need of serpentine 

 mobility, no prtetergal sclerites are definitely cut off from the 

 terga, though pairs of pr^esternal sclerites are developed. The 

 eyes may be lost ; when present they are invariably four in 

 number. The segments of the antenna never normally fall 

 below seventeen nor above about thirty. On the other hand, 

 the basal segments of the legs are feebly developed as 

 in the Geophilomorpha, and the toxicognaths are modified 

 and the pleural sclerite of the last leg-bearing somite en- 

 larged and fused with the basal segment of the appendage as 

 in the members of that order. 



Several families — Scolopendriidse, Newportiidee, etc. 



Order 3. — Craterostigmomorpha. 



Chilopods derivable from a primitive form of Scolopendro- 

 morpha (which was furnished with twenty-one pedigerous 

 somites, nineteen pairs of stigmata, complete penultimate and 

 antepenultimate segments on the toxicognaths, distinct tergal 

 plate for these appendages, and undivided tarsal segment 

 on all but the last pair of legs, which had the first segment 

 free), by the excalation of the sternal area and limbs of the 

 third, sixth, ninth, eleventh, fourteenth, and seventeenth 

 somites, thus reducing the number of legs to fifteen 

 pairs ; by the retention of six pairs of stigmata upon the 

 somites bearing the third, fifth, eighth, tenth, twelfth, and 

 fourteenth pairs of legs ; by the enclosure of the anal and 



