46 



SYDNEY EVANS JOHNSON 



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Fig. 41 Transverse section of the lateral sensory cord, of a 19 mm. specimen, 

 near its anterior end. The large lateral nerve has caused a slight bulging of the 

 overlying ectoderm. Squalus. X 592. 



^ ^ Fig. 42 Transverse section of the sensory cord of the same specimen as shown 

 in figure 41, further caudad. The fibers of the lateral nerve have separated into 

 four bundles. X 592. 



Fig. 43 Transverse section of lateral sensory cord at point indicated by the 

 line A-B in figure 38. Squalus, 20 mm. specimen. X 300. 



^ I^Fig. 44 Surface view, Squalus 21 mm. From a sketch by Otto Swezey. 

 X 8. 



Fig. 45 Dorso-lateral dissection of a similar stage. X 12. 



Twenty-one millimeter stage. An embryo 21 mm. long is 

 represented in figure 44. In it the structures described in pre- 

 vious stages are a little further advanced. Figure 45 shows a 

 partial lateral dissection of an embryo of the same age. The 

 ganglia of the seventh are exposed together with the nerves 

 that pass from them to the supra- and infraorbital lines. The 

 independence of the very elongated lateralis ganglion is clearly 

 exhibited. In this figure should be especially noted the nerve 

 trunk for the dorsal series of pit organs. 



