CONTRIBUTION TO THE EMBRYOLOGY OF THE 



LIZARD ; 



With especial Reference to the Central Nervous System and 

 some Organs of the Head; together with Observations on 

 the Origin of the Vertebrates. 



HENRY ORR, PH.D. 

 University Fellow in Biology at Princeton, N.J. 



INTRODUCTION. 



The embryology of the lizard has been investigated in parts 

 by various authors, yet all the work done on the subject is 

 hardly so complete as to warrant a monograph. Concerning the 

 segmentation of the egg and the formation of the germ-layers 

 we are indebted for our knowledge to Balfour} Hoffman^ and 

 Weldon? These earliest stages of development were lacking in 

 the material collected by me, so that my work begins about the 

 stage where that of Balfonr and Weldon ended, and deals with 

 the'^early development and differentiation of some of the organs. 

 The most comprehensive contribution hitherto made to lizard- 

 embryology is that of Hoffman. Strahl, in a series of articles 

 in the Arch. f. Anat. u. Phys. (Anat. Abth.) '81-87, has de- 

 scribed the relations of the amnion and some anatomical 

 features, but his methods prevented him from entering upon 

 details requiring a finer histological investigation. 



The material for the present investigations was collected by 

 me while a member of the zoological expedition generously 

 equipped and sent to Abaco, Bahamas, W.I., by the Johns 

 Hopkins University. The specimens have been kindly identi- 

 fied for me by Prof E. D. Cope. 



1 Balfour. — Ox).^^ Early Development of the Lacertilia, together with some Obser- 

 vations on the Nature and Relations of the Primitive Streak. — e««;'A Journ. of 

 yj//V. 5'c/.,Vol.XIX., N.S., 1879. 



2 Hoffman. — Weitere Untersuchungen z. Entw.-gesch. d. Reptilien. — Morpholo- 

 giscJies Jahrbuch, XI. Bd., 1885. 



3 Weldon. — Note on the Early Development of Lacerta Muralis. —Quart. Journ. 



of Mic. Sci., Jan., 1883. 



