EXPLANATION OF PLATES I, II, & III. 



Illustrating Mr. W. F. R. Weldon's Note on the " Early 

 Development of Lacerta muralis." 



In all figures : — pr. Primitive streak. 61. Blastopore, ep. Epiblast. hi/. 

 Hypoblast, c/i. Notochord. me. Primary mesoblast. me'. Secondary meso- 

 blast, budded off from lower layer cells, pp. c. Body cavity, i. c, m. Inter- 

 mediate cell mass. s. v. Segmental vesicle, lo. d. Wolffian duct. 



Fig. 1. — Median longitudinal section through a blastoderm vrith a primitive 

 streak, but no blastopore. 



Fig. 2. — Median longitudinal section through a blastoderm with a blasto- 

 pore visible as a pit at the anterior end of the primitive streak. 



Fig. 3. — An embryo in which the blastopore has just broken through. 

 Median longitudinal section. 



Fig. 4. — From an embryo slightly older than that shown in Fig. 3. 



Fig. 5. Lateral longitudinal section through the same embryo as that from 

 which Fig. 4 is taken, showing the forward growth of mesoblast from the 

 lips of the blastopore. 



Figs. 6 — 13. — A series of transverse sections through an embryo slightly 

 older than that shown in Figs. 4 and 5. The sections are in order from 

 behind forwards. 



Fig. 14. — Lougitudinal section through the posterior region of an embryo 

 in which the mesoblastic split is complete, to show the median posterior body- 

 cavity into which the allantois will project. 



Figs. 15 and 16. — Transverse sections through an embryo with seven proto- 

 vertebrae. Fig. 15, from the fifth protovertebra ; Fig. 16, from the inter- 

 vertebral region behind. 



Figs. 17 and 18.— From an embryo with ten protovertebrse. Fig. 17, verte- 

 bra ; Fig. 18, from the next intervertebra. 



Figs. 19 and 20. — From an embryo with eleven protovertebrse. Fig. 19, 

 vertebra ; Fig. 20, from the next intervertebra. 



Figs. 21 — 23. — From an embryo with twelve protovertebrae. The first of 

 these sections passes through a protovertebra ; the second through the next 

 intervertebral region behind the first ; and the third through the commence- 

 ment of the following protovertebra. 



Figs. 24 and 25.— From an embryo with fourteen protovertebras. Fig. 24, 

 from a protovertebra ; Fig. 25, from the next intervertebra. 



