THE LATER DEVELOPMENT OF THE FROG 157 



D 



FIG. 53. The development of the lateral line organs in R. sylvatica. After 

 Harrison. A. Part of a frontal section through the level of the notochord of a 

 3.3 mm. embryo. B. Part of a transverse section through the vagus region of a 

 4mm. embryo. C. Part of a frontal section through a 4 mm. embryo of R. 

 oirescens. D. Section through the lateral line organ of a 15.5 mm. larva of 

 R. sylvatica. a, Auditory vesicle (in A , its rudiment) ; b, basement membrane 

 of epidermis; ch, notochord; g, gut; gV, trigeminal ganglion, of V cranial nerve; 

 gVIII, acoustic ganglion of VIII cranial nerve; gX, vagus ganglion; gXl, ganglion 

 of the lateral nerve (branch of the vagus) ; i, intersegmental thickenings of the 

 epidermis (ectoderm) ; I, rudiment of lateral line nerve; Ip, lateral plate of meso- 

 derm; my, myotomes; n, inner or nervous layer of epidermis (ectoderm); nc, 

 nerve cord; p, pigment in epidermis; s, superficial layer of epidermis (ectoderm) ; 

 si, inner sheath cells of lateral line organ; sn, sensory cells of lateral line organ; 

 so, outer sheath cells of lateral line organ. 



