J. F. MCCLENDON. 



than in older .individuals. A further displacement of nerve cen- 

 ters results in that of the fourteenth segment being located in 

 the fifteenth. 



Stage 10. (Figs. 1 1-13.) This is the adult stage, and since 

 there is little change in the nervous system after the first moult, 

 except increase in size, it will apply equally well to young or old 

 individuals. 



I have not been able to add anything to the excellent work of 

 Saint-Remy and of Police (1901, 2) concerning the internal 

 structure of the nerve centers. The nervous system of the 



JP' 



'6A JP 3P 



FIG. 12. Tenth stage (adult), >( 34- Drawn from a plastic model of the cephalo- 

 thoracic nerve mass made with the aid of dissections and series of sections in three 

 planes. OL, lateral eye nerve ; OM, median eye nerve ; ./?, rostral nerve ; 2/ > , 

 cheliceral nerve ; 2P l , branches of cheliceral nerve ; $P, pedipalp nerve ; 3/", 

 branches of pedipalp nerve running parallel a short distance ; 4-11^, anterior nerves 

 of neuromeres four to eleven; 4-7, 9-1 iP, posterior nerves of corresponding 

 neuromeres. 



scorpion has been dissected and figured by many skilled ob- 

 servers, but in the light of my observations on the embryology 

 perhaps I may call attention to some facts of interest. 



Each cheliceral nerve (Fig. 12, 2.P) gives off two small 

 branches (2/ 31 ) just before piercing the outer neuriletnma. Pat- 

 ten figures two small nerves in this position which he calls the 

 " anterior and posterior haemal nerves " of this neuromere, but 

 from a study of their development I feel certain that they are 

 merely branches of the cheliceral nerve. 



Patten describes and figures a large ganglion in connection 

 with a branch of the pedipalp nerve and a branch of the " anterior 



