70 
ON A PLATYPUS EMBRYO, 
EXPLANATION OF PLATES. 
Reference Letters. 
am. a. Amniotic area. amc. v. Amnio -cardial vesicle, aud. Auditory 
plate, bl. Blastopore. bl. c. Blastoporic canal. bl. op. Internal opening 
of blastoporic canal. b.v. Blood vessels cw. Ccelom. d. Jr. Median 
sulcus of medullary plate (' ; Ruckenfurche "). ect. Ectoderm, ent. Ento- 
derm, ent. ph. Pharyngeal entoderm. h.a. Heart Anlage. h. pr. Head 
process of primitive streak, hp. mes. Head plate of mesoblast. lit end. 
Heart endothelium, le. Longitudinal strand of cells lying just external to 
the edges of medullary plate. m.s. Somite. m.s.c. Cavity of somite. 
md. f. Medullary fold. md. p. Medullary plate, mes. Mesoderm, mes. 
ax. Paraxial mesoderm in front of 1st somite, mes. I. Lateral mesoderm. 
N. Neurornere of mid-brain. n'-n. iv Neuromeres of hind-brain. nch. 
Notochord. nch.c. Remains of notochordal canal. op. (jr. Optic groove. 
pra. Proamnion, pr. g. Primitive groove, pr. s. Primitive streak, som. 
Somatic mesoderm, spl. Splanchnic mesoderm, vas. r. Vasifactive cells. 
vit. ent. Vitelline entoderm, iv. b. Anlage of Wolffian body. w. d. Anlage 
of Wolffian duct. w. t. Anlage of Wolffian tubules. 
Plate ix. 
Photo-micrograph of Platypus embryo from the egg just ready to be laid. 
From the dorsal surface. ( x 5*. ) 
Plates x.-xin. 
The positions of the sections from which figs. 1-13 are drawn are indicated 
in the photo-micrograph by corresponding numbers. 
All the drawings were made with a Zeiss' camera lucida. 
Plate x. 
Transverse section through the anterior end of the medullary plate, 
showiug its separation from the vesicle, the proamnion (pra.) 
underlying it and the amnio-cardial vesicles [amc. v. ) laterally, 
(x 70.) 
Transverse section of the middle region of the future fore-brain 
passing through the commencement of the optic groove {op. gr.). 
The median sulcus (d.fr.) will form the future medullary groove 
proper. ( x 70. ) 
Transverse section slightly posterior to fig. 2 showing the hollow 
outgrowth from the floor of the optic groove. ( x 70.) 
Fig. 2.- 
Fig. 3.- 
