ABSTRACT
The ontogenetic pattern of erythropoiesis in terms of its time of onset, distribution of loci, duration of activity at given sites and intensity of production would intuitively be expected to differ among species of birds. Conditions such as the normal length of incubation and the naturally occurring differences in the erythrocytic parameters of adults belonging to different taxa, for example, would seem likely to be associated with variations in erythropoietic ontogeny. Hepatic and splenic erythropoiesis begin in the bird on approximately the same day, that is after 75% of the incubation period has elapsed, while marrow erythropoiesis starts on the day before hatching i.e., after 90% of its incubation has been completed. The comparable values for the initiation of hepato-splenic erythrocytic production in the chick are after 33–38% of the term of incubation has been completed and after 60% of the incubation period has been expended for the commencement of marrow erythropoiesis.
