June, 1916] Epibranchial Placodes of Squalus Aca?ithias 345 



EXPLANATION OF FIGURES. 



All drawings were made from the posterior surfaces of 10 micron sections, 

 with a camera lucida. Outline drawings were magnified oOx; high power draw- 

 ings were magnified 620x. All figures were reduced to one-third the original size 

 in reproducing. The sections are numbered serially from anterior to posterior, 

 showing the relations of the sections used in the drawings. 



KEY TO ABBREVIATIONS. 



Aud. — Auditory vescicle. 



Ec. — Ectoderm. 



G. C— Gill cleft. 



G. V. VII — General visceral portion of the seventh ganglion. 



G. V. IX — General visceral division of the ninth ganglion. 



G. V. Xi, Xa, X3, X4 — General visceral divisions of the first, second, third and 



fourth epibranchial ganglia of the tenth nerve. 

 G. X — The main ganglionic mass of the X nerve. 

 L. IX — Lateral line portion of Gang. IX. 

 L. X — Lateral line portion of Gang. X. 

 L. PI. — Lateral line placode. 

 M. — Metencephalon. 

 PL— Placode. 



S. V. VII — Special visceral portion of Gang. VII. 

 S. V. IX — Special visceral portion of Gang. IX. 



S. V. X — Special visceral portion of the main ganglionic mass of the X nerve. 

 S. V. Xi, X2. X3, X4 — Special visceral divisions of the first, second, third and 



fourth epibranchial ganglia of the X nerve. 

 V. — Blood vessel. 

 V. L. VII — Ventral lateral line division of Gang. VII. 



