Op^'iO 



r ~ -iCOC. 



pro- 1 





o-'>p--Jf- 



^eox.gl- 



pet.--S- 





-(/OM. 



co- 



rnet. 



Fig. 352. The development of the Arachnida. A, Transverse section of a spider 

 embryo (Theridium), after Morin, showing the coelomic sacs (coe.) and the 

 formation of the heart (h.). n.r. nerve rudiment ; y. yolk with contained cells. 

 B, Sagittal section of a spider embryo after Wallstabe. Coelomic sacs of 

 pre. precheliceral segment, pro. i, pro. 6, first and last limb-bearing segments 

 of the prosoma, prg. pregenital segment, op. 2, second, and op. 10, tenth seg- 

 ment of the opisthosoma. C, Diagram of the scorpion embryo, altered from 

 Dawydoff. Coelomic sacs of pre. precheliceral segment; 1-6 limb-bearing 

 segments of the prosoma; prg. pregenital segment; gop. segment of genital 

 operculum ; pet. segment of pectines ; Igp. segments of first three lung books ; 

 eo.d. coelomoducts which never reach the exterior; cox.gl. coxal glands; gon. 

 gonoducts; g. gonad. D, Embryo of the scorpion Buthus earpathieus, after 

 Brauer. Stage showing che. the chelicerae; pp. pedipalps; the four other 

 appendages of the prosoma; prg. the pregenital segment and appendages; 

 8, appendage forming genital operculum, succeeded by those which form 

 the pectines and the lung books; 13, last of these; 7net. metasoma. 



