TRACHEA TA 313 



lies just behind the cephalic shield, gives off a median and two 

 lateral vessels ; the former supplies the head and mouth parts, 

 the latter form a ring round the oesophagus and unite to form 

 a ventral vessel which lies above the nerve cord. These vessels 

 open into lacunae, which ultimately communicate with the 

 body-cavity, and from this the blood returns to the heart 

 through paired valvular openings in each chamber. The heart 

 is supported by a pericardium, to which are attached certain 

 muscles, the alae cordis ; these arise from the body- wall. The 

 blood is colourless, and contains numerous white corpuscles. 



A pair of stigmata are found on the third, fifth, eighth, 

 tenth, twelfth, and fourteenth leg-bearing segments, situated on 

 the soft tissue between tergum and sternum, immediately 

 behind the base of each leg. Each stigma opens into a swollen 

 sac, which gives off two main tracheae and a number of smaller 

 ones, which supply the neighbouring parts. The arrangement 

 of the larger branches varies in the anterior and posterior ends 

 of the animal, but two main branches are usually present, one 

 running dorsally, the other ventrally; they divide into smaller 

 and smaller branches, and ultimately form a network which 

 ramifies through every organ of the body. The tracheae are 

 kept open by a spiral thickening of their chitinous lining. 



The ventral nerve cord bears sixteen ganglia, each of which 

 gives off three nerves on each side to the legs and adjacent 

 muscles. The first of these supplies the poison claws; the 

 cord is connected by circum-oesophageal commissures ending in 

 the bilobed cerebral ganglion which gives nerves to the eyes, 

 antennae, and mouth organs. When a basilar segment is pre- 

 sent, the corresponding ganglia are fused together. In some 

 Ghilopoda the first few ganglia of the ventral nerve cord are 

 more or less completely fused; some writers have held that 

 this indicates a division of the segments of the body into 

 thorax and abdomen. Besides the eyes, sensory hairs are found 

 on the antennae, and in Scutigera there is a peculiar sense organ 

 on the ventral part of the head consisting of a pouch lined with 

 sensory hairs, each of which is connected with a nerve fibril. 



ZithoMus is dioecious, and the generative organs usually 

 attain their full size during the spring. The testis consists of 

 a blind tube, the lining cells of which give rise to the sperma- 



