228 



Arthropoda. 



one pair of antennae, whicli are simply filiform or feebly clavate, 

 and tlie usual three pairs of jaws, or two only. The body is 

 not divided further into regions, but consists usually of a large 

 number of essentially similar segments, which bear short cylindrical 

 legs, each composed of a simple series of joints (6 — 7). 



The Myriapoda resemble the Tnsecta in their internal structure. 

 The alimentary canal is generally straight, and is divided 

 into a narrow CBsophagus, a cylindrical mesenteron, and a narrower 

 hind-gut ; salivary glands open close to the mouth ; at the junction 

 of the mesenteron and hind-gut, open two (or more rarely four) 

 Malpighian tubules (c/. Insecta) ; the anus is in the terminal 

 segment. There is no liver. The heart is a long dorsal tube 

 with paired lateral slits, through which blood enters ; it gives off an 

 anterior, and a series of lateral arteries, whilst the 

 blood also flows through the various slits and spaces 

 of the body. The Myriapods, like Insects, have a 

 system of air-carrying tubes, a tracheal system, 

 which ramifies throughout the body, and opens by 

 stigmata, generally at the base of certain of the 

 pairs of legs. The aervous system is of the 

 usual arthropod type ; the ventral nerve ganglia are 

 generally equally developed in correspondence with 

 the uniform development of the body segments. The 

 ovaries or testes are always fused into an 

 unpaired organ, which in the Chilopoda, opens 



Pig. 191. 



Fig. 190. 



Fig. 190. Digestive tract of Lithohius (Chilopoda). a anus, 

 h hind-gut, m mesenteron, s saliyary gland, u Malpighian tubule, 

 -After Plateau. 



Fig. 191. Newly-hatched larva of a Diplopod. — After Metsch- 

 nikoff. 



ventrally at the end of the body, in front of the anus, by a single 

 aperture ; whilst in the Diplopoda, a pair of genital pores lies between 

 the second and third pairs of legs, and thus far forward on the 

 ventral side of the body. In this last group, the limbs of the 

 seventh segment are usually modified in the males, to form copulatory 



