DESCRIPTION OF PLATE III, 



Illustrating paper on the ''Early Development of the 

 Lacertilia, together with some Observations on the 

 Nature and Relation of the Primitive Streak." 



Complete List of Reference Letters. 



m.g. Medullary groove. me. p. Mesoplastic plate. ep. Epiblast. 

 Ay. Hypoblast. ch'. Notocliordal thickening of hypoblast. ch. Noto- 

 chord. ne. Neurenteric canal (blastopore), pr. Primitive streak, am. 

 Amnion. 



Series a.— Sections through an embryo shortly after the formation of the 

 medullary groove. X 120.' 

 Pig. 1.— Section through the trunk of the embryo. 

 Figs. 2 — 5.— Sections through the neurenteric canal. 



Pig. b.— Surface view of a somewhat older embryo than that from which 

 Series a is taken. X 30. 



Series b.— Sections through the embryo represented in Pig. b. X 120. 

 Pig. 1.— Section through the trunk of the embryo. 

 Figs. 2, 3.— Sections through the hind end of the medullary groove. 

 Pig. 4. — Section through the neurenteric canal. 

 j'iG. 5. — Section through the primitive streak. 



Pig. c— Surface view of a somewhat older embryo than that represented 

 in Fig. b. X 30. 



The spaces between the layers in these sections are due to the action 

 of the hardening reagent. 



