928 THE AMERICAN NATURALIST.  [Vor. XXXIV. 
position and shape of the limb anlages are shown in Fig. 1, and 
the section demonstrates that they are formed by mesoderm, 
with a thin covering layer of ectoderm. The mesoderm is 
Spc. D.R. G. 
Í 
Fic. 6. — Pig of 120 mm. No. 5. Transverse section 470. Ao.S., left dorsal aortic trunk; 
cesophagus; X.D., ramus dorsalis of spinal nerve; A 
nerve ; S.a.c., septum of auricular canal; Sci. V., EEE ; Som., somatopleure ; 
ae spinal cord; S.s., — is eme Tra., ane chea y Val, ;atrio-ventrcular valve ; 
7..5., left ventricle; V.R., 
very little differentiated, none of the skeletal elements being 
yet formed. The nerves and blood vessels are growing into 
