lOO PERIPHERAL NERVES AND GANGLIA. 



divides into three nerves which then subdivide into motor and sensory branches 

 (for details, see original memoir, 1893). 



The hamal nerves (Fig. 70, h.n' and h.n^), pass out of the endocranium 

 through the occipital ring and are distributed to the sides of the body, between the 

 sixth pair of legs and the operculum. For the distribution of the intestinal and 

 cardiac branches, see pp. 103, 200. 



Scorpion. 



In the scorpion, the vagus region consists of four metameres, two genital, 

 one pectinal, and the first branchial, as I demonstrated in my first paper on this 

 subject, 1889. 



The tergite of the first metamere fuses with the thorax and cannot be detected 



Fig. 73. — Af Section of an abdominal neuromere of a new-bom scorpion, showing the ganglionated *' dorsal," 

 or neural, nerve root; B; same through the non-ganglionated h£emal nerve root; C, section of the second free 

 branchial neuromere of an adult scorpion, showing both neural and heemal nerve roots and the neural and haimal 

 transverse commissures; D, third branchial neuromere of an old embryo of a scorpion, showing the large ganglionic 

 lobe at the root of the neural nerve. 



in the adult. The other three tergites remain separate throughout life, the second 

 or genital, and the third or pectinal, being much narrower than the fourth (Fig. 17). 

 The fusion of these metameres is more strongly marked on the neural than on the 

 haemal surface. 



During the early embryonic stages, one may recognize four distinct pairs of 

 rudimentary, abdominal appendages (Figs. 15, 16). During the later stages, 

 the first lung book appears in place of the last appendage. The third pair gives 

 rise to the pectines; the first pair disappear altogether by the time of hatching; 

 while the second pair finally unite in the median line in front of the pectines to 

 form the genital cushion, or tubercles. 



Before they unite, about stage G (Fig. 16, B), the genital openings may be 



