ABBREVIATIONS 



AP, ascending process of a neurone MC, muscle cell 



C, notochord P, pigment 



CC, central canal of the spinal cord S, spinal cord 



DC, giant ganglion cell of the dorsal SG, anlage of the spinal ganglion 



column VC, cell of motor column 



DP, descending process of a neurone VF, ventral root fiber 



DT, the tract of the giant ganglion VT, ventro-lateral tract of the somatic 



cells, dorso-lateral tract motor column 



M, myotome Y, yolk globule 



All the figures have been drawn with the aid of the camera lucida. In all but 

 figures 6 and 8, with which lower magnification was required, the lenses employed 

 with the camera were the Zeiss Homog. oil-immersion 2 mm. objective and Com- 

 pensating ocular 6. In nearly every case the compensating ocular 12 was intro- 

 duced for critical study in the completion of the drawings. The numbers intro- 

 duced in parenthesis in the explanation of particular figures record the serial 

 number of the specimen in the collection, the number of the slide and section. 

 In all figures from longitudinal sections 'the upper end of the drawing as it is 

 arranged on the plate is directed rostrad in the animal. 



Fig. 1 From a specimen (545, 1-6-8) which reacted to electrical but not to 

 tactile stimulation; fixation. Van Gehuchten's fluid (alcohol-chloroform-acetic 

 acid); stain, erythrosin and toluidin blue; sections, 5 m, in the frontal plane. 



Fig. 2 From a specimen (546, 6-3-2) of the same description and treated with 

 the same methods as the last. 



Fig. 3 From a specimen {476, 1-2-20) of the early flexure stage; fixation, subli- 

 mate-acetic; staining, alum carmine in toto and Lyon's blue in 95 ppr cent alcohol ; 

 sections, 10 n, in the frontal plane. 



Fig. 4 From the same specimen (476, 1-2-16) as the last. 



Figs. 5 to 6 From a specimen (475, 2-1-8) of the same description and treat- 

 ment as the last. 



Figs. 7 to 8 From the same specimen (475, 1-3-12) as the last. 



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