570 E. RAY LANKESTEB. 



somite carry appendages modilied as ruaxilla?. The fourth 

 post-oral somite has its appendages converted into very large 

 and powerful hcmignaths, which are provided with poison- 

 glauds. The remaining somites carry single-clawed walking 

 legs, a single pair to each somite. The body is anomomeristic, 

 showing in different genera from 17 (inclusive of the anal 

 and genital) to 175 somites behind that which bears the 

 poison-jaws. No tagmata are developed. The genital ducts 

 open on the penultimate somite. 



Trachea3 are developed which are dendriform and with 

 spiral thickening of their lining. Tlieir tiunks open at paired 

 stigmata placed laterally in each somite of the trunk or in 

 alternate somites. Usually the trachese open by paired 

 stigmata placed upon the sides of a greater or less number of 

 the somites, but never quite regularly on alternating somites. 

 At most they are present on all the pedigerous somites except- 

 ing the first and the last. In Scutigera there are seven 

 unpaired dorsal stigmata, each leading into a sac, whence a 

 number of air-holding tubes project into the pericardial 

 blood-sinus. 



Renal ca^cal tubes (Malpighian tubes) open into the procto- 

 dasum. 



Class 5. — Hexapoda. 



Head shown by its early development to be triprosthome- 

 rous, and consequently tetartognathous. The first prostho- 

 mere has its appendages represented by the compound eyes 

 and a protocerebrum ; the second has the antennas for its 

 appendages and a deutocerebral neuromere; the third lias 

 suffered suppression of its appendages (which corresponded 

 to the second pair of antennae of Crustacea), but has a trito- 

 cerebrum and coelomic chamber. The mandibular somite 



prosthomcre of centipedes has its appendages reduced and represented only 

 by e^e-patclies (as in Aracluiida, Crustacea, and lloxa))oda), llie second lias a 

 rudinienlary antenna, wliicli disappears, whilst the third carries the permanent 

 auteuuse, which accordingly correspond to the second anlcnuBe of Crustacea, 

 and are absent in Hexapoda. 



