XI 



PHYLUM ARTHROPODA 



fi07 



of antennae probably correspond to the antennules of the Crayfish 

 the antennae 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. COCKROACH. 



Antennules. 

 Antennae. 

 Mandibles. 

 First maxillae. 

 Second maxillae. 

 First maxillipedes. 

 Second maxillipedes. 

 Third maxillipedes. 



Antennae. 



Absent. 



Mandibles. 



First maxillae. 



Second maxillae (labium) 



First legs. 



Second legs. 



Third legs. 



add.cox 



abd.ccac 

 cxi.Jem 



Kepresentatives 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 respiratory movements are to be 

 observed, in which the abdomen becomes alternately expanded 

 and contracted ; these move- 

 ments bring about the alternate 

 inhalation and exhalation 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 

 between the prothorax and meso- 

 thorax, and the other between 

 the mesothorax and the meta- 

 thorax. Eight occur on either 

 side in the abdomen between the 

 terga and sterna of the seg- 

 ments. Just internal to each 

 spiracle the main air-tube or 

 trachea into which it leads pre- 

 sjjnts an elastic ring or spiral, 

 acting as a valve for closing the 

 passage. 



The principal Sets of mUSCleS p ia . 501. Ventral portion of the muscular 

 f ^ trnnlr nf fhp fWlrrnarh arp system of the Cockroach, add.cox. ad- 

 ductor of coxa ; abd. cox. abductor of coxa ; 



(1) the longitudinal Sternal mUSCleS ext fern, extensor of femur ; 1st terff stern. 

 }'. ~~-,7 \ i -I p first tergo-sternal ; long, stern, longitudinal 

 (Fig. 501, long. Stem.), Which form sternal ; obi. stern, oblique sternal. (After 



a transversely segmented sheet, Mia11 and Denny -> 



extending between adjoining sterna of the thorax and abdomen ; 



(2) oblique sternal muscles (obi. stern.}, confined to the abdomen ; 



long, stern 



M. stern 

 terg.stern, 



