NO. 6 ANNELIDA, ONYCHOPHORA, AND ARTHROPODA SNODGRASS 6l 



The onychophoran brain thus appears to contain, as Hanstrom 

 (1935) has shown, a mixture of polychaetous and arthropodan char- 

 acters. Its origin must be found in the annehd brain ; but certain 

 pecuhar features of the onychophoran brain would seem to prechide 



Stom 



Fig. 27. — Developmental stages of various head structures of Onychophora. 

 (A, C from Kemiel, 1888; B, D, E from Evans, 1902.) 



A, cross-section of head of embryo of Pcripatus edzvardsi Blanchard through 

 jaws (/), showing groups of brain cells proliferated from ventral organs (2V O) 

 of jaw somite. B, cross-section of embryonic head of Eoperipatus iveldoni 

 Evans, showing coelomic sacs of antenna embracing the stomodaeum, and gen- 

 eration of brain (Br) from cephalic ventral organs (iVO). C, section through 

 anterior part of head of embryo of Peripatus cdzuardsij showing antennal coelomic 

 sac extending into antenna. D, section of embryonic head of Eoperipatus iveldoni 

 with canal {d) from antennal coelom opening mesad of circumoral fold (cof). 

 E, same, more anterior section, showing antennal coelomic sacs, and a pre- 

 antennal sac on left side. 



Ant, antenna; AntCoel, coelomic sac of antenna; AntNv, antennal nerve; 

 Br, brain ; cof, circumoral fold ; Cpr, coelomopore of antennal coelom ; E, pit 

 of developi'ig eye; Ecd, ectoderm; End, endoderm ; He, haemocoele ; /, jaw; 

 mcl, muscles of stomodaeum, Mcnt, mesenteron (folded forward on stomo- 

 daeum) ; PrntCoel, preantennal coelom; Stom, stomodaeum; iVO, preoral 

 cephalic ventral organ; 2V O, ventral organ of postoral jaw somite; Y, yolk. 



the possibihty of its having given rise to the arthropod brain. The 

 superficial position of the antennal nerve tracts (fig. 25 A, C, AntT), 

 which traverse the forebrain dorsal to the optic lobes (A, OpL), con- 

 stitutes a condition quite at variance with that in any arthropod, for 

 in all the Arthropoda the antennal nerves issue from antennal lobes 



