434 



ARTHROPOD A 



of appendages, a pair of several-jointed mandibles (fig. 491), and a pair of 

 rudimentary maxilla- fused to a single plate, the gnathochilarium. 



The gonads lie ventral to the intestine far back in the body, those of the right 

 and left sides enclosed in a single sac; the ducts open separately on the second 



FIG. 490. FIG. 491. 



FIG. 490. Schematic section of Diplopod (compare with fig. 439). </, digestive 

 tract; g, gonad; /;, heart; r, repugnatorial gland; s, spiracle and trachea?. 



FIG. 491. Mouth parts of lulus (after Latzel). 2, mandibles of 7. molybdinus; 

 3, gnathochilarium (fused maxilla;) of 7. luridus. 



somite of the trunk. The spermatozoa are not motile. The legs of the seventh 

 segment of the male are used in copulation. The young escape from the egg 

 with three pairs of legs, a point once thought to show resemblances to the 

 Hexapoda, but which does not, for these legs are on the fourth, sixth, and 

 seventh somites of the body. IULID^E, elongate cylindrical bodies; Spirobolus.* 



FIG. 492. lulus maximus (after Schmarda). 



GLOMERID.E short, capable of rolling into a ball; POLYDESMID.E. PAUROPODA: 

 minute; body with twelve segments, tending to fuse to six. Pauropiis* More 

 uncertain in position are the SYMPHYLA (Scolopendrella*) ; from the position of 

 the genital opening they are placed here. 



Summary of Important Facts. 



1. The ARTHROPODA are animals with evident internal and 

 external segmentation (metamerism) . 



2. The metamerism is expressed internally in the muscles, in the lad- 

 der-like nervous system, in the structure of the heart, and in the arrange- 

 ment of segmental organs and tracheae so far as these are present. 



