4 A. 



5Pi ^-5 A 



. . '.' '- ' '.' D 



- ^'. : ... % - ' . -. , 



S ' 



' :: --.:-.:.: : -' : ' : I ' 



\v?;ffS';; ; v :; -; 



.'-ilf ^r-l4 



'-: ^P ;; !/! 

 ^'''/j' ' 



a 



FIG. 6. Sixth stage of same, X45- The cephalo-thoracic appendages have been 

 removed. Some of the details have been filled in from a study of serial sections. 

 a, anus ; ab 2 , second abdominal appendage ; et, anterior border of ectoderm grow- 

 ing over first neuromere ; mx, maxillaria ; n 20 , twentieth neuromere ; ol, lateral eye ; 

 si, semilunar lobe ; 4-13,4, anterior nerves of fourth to thirteenth neuromeres ; 3-7, 

 9-l$P, posterior nerves of corresponding neuromeres ; 20, twentieth body segment. 



FIG. 7. Seventh stage of same, X 45- Cephalothoracic appendages removed ; a, 

 anus; ab 2 , second abdominal appendage ; ch l , articulation of the chelicera ; 19 + 2 , 

 fusion of the nineteenth and twentieth nerve centers ; ol, lateral eye ; omo, common 

 neck of the two median eye sacs ; 15-20, fifteenth to twentieth body segments. 



