XI 



PHYLUM ARTHROPODA 



575 



the antenna' of the latter not being represented. On this view 

 the homologies of the anterior appendages in the two animals may 

 be expressed in the following table : 



CRAYFISH. 



Antennules. 

 Antenna?. 

 Mandibles. 

 First maxilhe. 

 Second maxilla?. 

 First maxilliped.es. 

 Second maxillipedes. 

 Third maxillipedes. 



COCKROACH. 



Antenna?. 



Absent. 



Mandibles. 



First maxilla?. 



Second maxilla? (labium). 



First legs. 



Second legs. 



Third legs. 



L 



aMccj 



J'-'ttrg. stern 



Representatives of the five pairs of thoracic legs of the Crayfish 

 would thus appear to be absent in the Cockroach, and evanescent 

 rudiments, no traces of which remain in the adult, alone represent 

 in the latter the well-developed 

 abdominal appendages of the 

 former. 



In the living Cockroach re- 

 spiratory movements are to 

 be observed, in which the ab- 

 domen becomes alternately ex- 

 panded and contracted ; these 

 movements bring about the 

 alternate inhalation and ex- 

 halation of air through certain 

 apertures the stigmata at 

 the sides of the body. Two 

 of these are situated on each 

 side of the thorax, one be- 

 tween the prothorax and meso- 

 thorax, and the other between 

 the mesothorax and the meta- 

 thorax. Eight occur on each 

 side in the abdomen between 



the terga and Sterna of tile FK.. 4.-.U. Ventral portion of the muscular 



T i svstem of the Cockroach. '"'-'. cox. a<l- 



Segments. Just internal tO ductor of coxa ; aM. cox abductor of coxa ; 



!-->-> r>V> cuiraplp ttip main tvMphp-t '''' ''-"' extensor of femur ; 1st terg. stem. 



first tergo-sternal; lonft. stc;-,i. longitudinal 



into which it leads presents an sternal; obi. stern. nl,li.|iu sternal. (After 



... i Miall and Dennv.) 



elastic ring or spiral, acting as 

 a valve for closing the passage. 



The principal sets of muscles of the trunk of the coekroach 

 are (1) the longitudinal sternal muscles (Fig. 456, long, stern.}, 

 which form a transversely segmented sheet, extending between 

 adjoining sterna of the thorax and abdomen; (2) oblique sternI 



long. ster. 



chl stern 

 lerif. stern 



