'\jJiO 

 [0 I 



PREFACE. ( ^93 



The following study, carried out in the 

 New York Ophthalmic and Aural Institute at 

 Prof. Knapp's suggestion, is based upon the 

 examination of a great number of specimens. 

 The chick-embryos were obtained by incu- 

 bation, and were hardened in Kleinenberg's or 

 Miiller's fluid, and stained with carmine and 

 hematoxylin-eosin. The pig-embryos were 

 obtained fresh and hardened in Midler's fluid, 

 after decalcifying, when necessary, with 

 phloroglucin or hydrochloric acid mixtures, 

 and the sections were stained mostly with 

 hematoxylin-eosin. Some of the breaks in my 

 series were supplied by Dr. B. Alex. Randall 

 of Philadelphia who kindly lent me a number 

 of his specimens, prepared by Dr. Piersol. 



W. A. H. 



37 West 39TH Street, New York, 

 Augtist 75-, i8gj. 



iii 



