NO. 6 ANNELIDA, ONYCHOPHORA, AND ARTHROPODA SNODGRASS 63 



stomodaeal musculature ; anteriorly they extend into the antennae 

 (C, AntCoel), and thus show their relation to these appendages. 

 According to Evans, the antennal sacs acquire temporary coelomo- 

 ducts (D, d) opening ventrally to the exterior (Cpr) within the 

 circumoral fold (cof). With the increase in the size of the brain, 



Fig. 28. — Structure of the onychophoran eye. (A, B, F from Dakin, 1921.) 



A, vertical longitudinal section of eye of Peripatoides occidcutalis Fletcher, 

 right half of retina depigmented. B, a retinal cell, differentiated into basal 

 ■plasmatic part {d) and distal optic rod (c). C, D, E, diagrams of development 

 of an eye of the vesicular type (see also fig. 19 G). F, tangential section 

 through optic rods of retina. 



a, b, outer and inner layers of corneal epidermis ; Br, brain ; c, optic rod of 

 retinal cell ; Cor, cornea ; Ct, cuticula ; d, basal plasmatic part of retinal cell ; 

 e, striated border of optic rod ; Epd, epidermis ; Ln, lens ; mcl, muscle fibers ; 

 «/, nerve fiber; Nu, nucleus; OpNv, optic nerve; OpV, optic vesicle; Pig, 

 pigment ; Ret, retina. 



the antennal sacs become reduced until finally, Evans says, they appear 

 only as two small spaces situated above the brain in front of the eyes. 

 A pair of small mesoderm masses observed by Evans in an embryo 

 of Eoperipatus iveldoni, lying above and before the antennal sacs, in 

 one of which a cavity was present (fig. 27 E, PrntCoel), are regarded 

 by Evans as representing a pair of preantennal coelomic sacs, possibly 



