JOURNAL OF MICROSCOPICAL SCIENCE. 



DESCRIPTION OF PLATE XIX, 



Illustrating Mr. F. M. Balfour's paper ou the " Early 

 Development of the Lacertilia, together with some 

 Observations on the Nature and Relation of the Pri- 

 mitive Streak." 



Complete List of Reference Letters. 



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

 hi/. Hypoblast. ch'. Notochordal thickening of hypoblast. ch. Noto- 

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

 Amnion. 



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

 medullary groove, x 120.' 

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

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

 Fig. 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 Fig. b. x 120. 



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



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



Fig. 4. — Section through the neurenteric canal. 



Fig. 5. — Section through the primitive streak. 

 Fig. c. — Surface vievr 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. 



