DEVELOPMENT^OP THE HEART IN MABSUPIALS. 



475- 



somite). Behind this again there are, as in Stage III., inter- 

 segmental offshoots from the dorsal aoita, but asyet no continuous; 

 vessel in this region. 



Text-figure 14. 



^■A: 



^C.Af^ 



-3<' 



yif/=, 



Perameles nasuta (2 P, A). Transverse section througli ventricular 

 region of the heart. 



^2- Second aortic arch. ^.F. Auditory vesicle. J) .^. Dorsal aorta. JE»i«i. Endo- 

 thelium. M.P. Medullary plate. My. Myocardium. V.C.M. Vena capitis- 

 medialis. 



Text-fififure 15. 



Perameles nasuta (2 P, B). 

 Longitudinal section, median through the anterior end of the embryo. 

 JEnd. Endothelium. P.P. Fore-brain. P.G. Fore-gut. M.P. Mid-brain. 

 M.M.P. Margin of medullary plate. My. Myocardium. O.P. OralJ'plate. 

 P. Pericardium. 



In this stage the Cuvierian ducts are recognisable lying in' 

 the somatopleure opposite the third somite and immediately 

 Proc. Zool. Soc— 1915, No. XXXIII. 33 



