78 AGE, GROWTH, AND DEATH 



its maximum, No. 3, and the corpuscle is in the 

 Ichthyopsidan stage, 1 which means the stage which 



FIG. 25. LIFE HISTORY OF BLOOD CORPUSCLES, RABBIT EMBRYOS. 



No. I. Embryo of 8 days, 6 hours, No. 883. No. 2. Embryo of 9 days, 

 No. 621. No. 3. Embryo of 9 days, 12 hours, No. 567. No. 4. Embryo of 

 10 days, No. 940. No. 5. Embryo of n days, No. 556. No. 6. Embryo of 

 14 days, 1 8 hours, No. 143. No. 7. Embryo of 16 days, 12 hours, No. 1229. 

 No. 8. Embryo of 18 days, No. 167. 



is permanent and the highest attained in fishes and 

 amphibians. The next stage, No. 4, is characterised 

 by a shrinkage of the nucleus, a degenerative change, 

 but bringing the physiological advantage of more 

 room for haemoglobin in the corpuscles. When the 

 nucleus shrinks it loses the granular appearance it 

 had before and also stains more deeply with the mi- 

 croscopists' dyes, Nos. 5 and 6. This is called the 

 Sauropsidan stage, 1 because it is that which is per- 

 manent and the highest attained in reptiles and birds. 



1 C. S. Minot, " Morphology of the Blood Corpuscles," Proc. Amer. Assoc. 

 Adv. Science, xxxix. (1890), p. 341, and Anatomischer Anzeiger, v., p. 601. 



