40S F. L. LANDACRE 



EXPLANATION OF FIGURES 



79 to 83 are reconstructions of the cranial ganglia of A. melas and are true in 

 two dimensions, the anterior-posterior and the dorso-ventral. The reconstructions 

 were made by projecting the section of the ganglion on paper to determine the 

 vertical length of a given section. The lens of the eye, which is an almost perfect 

 circle in these diameters, was used as a basis for determining the ratio of longitudi- 

 nal to vertical dimensions. The reconstructions give an approximately exact 

 picture of the lateral view of the ganglia as seen on a flat surface. The figures 

 give no idea of the relative thickness of the ganglia and many of the roots appear 

 as large as the ganglia while in reality they are quite thin, sometimes not more than 

 one cell thick, cf. the roots of the II, III and IV epibranchial ganglia, figs. 79, 80 

 and 81. The object in making these reconstructions was to trace the embryonic 

 ganglia up to a stage where they could be positively identified as the definitive 

 ganglia of the adult. 



79 is a reconstruction of the ninth and tenth ganglia of A. melas, SI hours; only 

 three epibranchial placodes are present at this stage. 



SO is a reconstruction of the ninth and tenth ganglia of A. melas, 93 hours. Four 

 epibranchial placodes are here present. 



81 is a reconstruction of the eighth, ninth and tenth ganglia of A. melas 138 

 hours. All placodes have disappeared some hours previous to this stage. 



