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SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 97 



thickened, but they have no differentiated gangHa, since the neuro- 

 cytes are scattered along their lengths. The brain, on the other hand, 

 is a well-developed, bilobed cerebral body (fig. 25 A, B) extending 

 horizontally forward from the anterior ends of the nerve cords (C). 

 It bears anteriorly the large antennal nerves (AntNv), laterally a 

 pair of small optic lobes supporting the eyes (E), and ventrally a 

 pair of small pear-shaped bodies (B. C. iVO). Numerous other 



Ant 



SIO3 



iL 



lU' 





--4-V0 



A 





B 



IVO 



2V0 )Q^i -'Xn )^ 



PrC " 



Fig. 23.-— Development of the onychophoran head and anterior body region 

 as shown in three embryonic stages of Pcripafus cdivardsi Blanchard, ventral 

 view. (From Kennel, 1888.) 



A, young embryo with large prostomial cephalic lobes, postoral jaw appen- 

 dages (/) and oral papillae {OP) resembling legs. B, older embryo with 

 prostomial antennal rudiments, jaws approaching mouth and surrounded by 

 circumoral fold (fo/), ventral organs (FO) becoming differentiated. C, still 

 older embryo ; jaws with definitive form, retracted into preoral cavity, ventral 

 organs more distinct ; head region composed of procephalic lobes, jaw somite, 

 and somite of oral papillae. 



ajVO, anterior ventral organ of papillar somite; cof. circumoral fold; /, jaw; 

 L, leg ; Lin, labrum ; Mth, mouth ; OP, oral papilla ; PrC, preoral mouth cavity ; 

 Prsf, prostomium; P3VO, posterior ventral organ of papillar somite; SIO, orifice 

 of salivary gland; iVO, ventral organ of preoral cephalic lobe; 2V O, ventral 

 organ of jaw somite; 3VO, ventral organ of somite of oral papillae (subdi- 

 vided into anterior and posterior parts) ; 4VO, 5VO, ventral organs of first and 

 second leg somites. 



small nerves are given off from the brain (fig. 24 A), among which 

 are anterior ventral nerves that go to the mouth and the circumoral 

 fold, a dorsal median nerve (/) that turns downward and posteriorly 

 on the dorsal surface of the stomodaeum, a pair of posterior stomo- 

 daeal nerves (/), and the nerves of the jaws (;'), which arise from 

 the nerve cords just behind the brain. 



The entire central nervous system of the Onychophora is developed 

 in the embryo from a series of paired ventral thickenings of the 

 ectoderm known as the "ventral organs" (fig. 23 B, C, VO), which 



