EXPERIMENTAL STUDIES ON THE DEVELOPMENT 



OF ORGANS IN THE EMBRYO OF THE 



FOWL (CALLUS DOMESTICUS). 



FRANK R. LILLIE. 



II. THE DEVELOPMENT OF DEFECTIVE EMBRYOS, AND THE 



POWER OF REGENERATION. 1 



Born has shown that young embryos of the frog possess im- 

 mense power of healing smoothly cut wounds, and that the 

 vitality of even small isolated parts is remarkable ; pieces of the 

 head or of the tail, for instance, may continue to grow and de- 

 velop in spite of the complete absence of the heart, blood and 

 blood vessels, and nervous system, for a period of about three 

 weeks, or until the yolk contained in the cells is fully consumed. 

 " The development of each organ progresses as far as the cut 

 surface as well as in the normal larva, no matter what the posi- 

 tion of the cut surface may be ; the absence of the heart or the 

 brain does not affect the subsequent processes of growth and dif- 

 ferentiation in any marked way." 



These conclusions are of great importance for the physiology 

 of development. So far as I know, similar experiments have not 

 been performed on the embryos of Auuiiota, and the following 

 account may serve to fill up the gap in part. Striking differ- 

 ences appear between the embryo of the fowl and of the frog in 

 regard to the vitality of defective embryos, or of parts of embryos : 

 The chick embryo dies very rapidly after destruction of the 

 heart, for the embryonic tissues are dependent to an extreme de- 

 gree upon the circulation ; it therefore follows that small parts of 

 an embryo cannot undergo differentiation as in the frog. On the 

 other hand, the growth of the extra-embryonic blastoderm is inde- 

 pendent of blood supply, and may continue in eggs in which there 

 is no embryo owing to destruction of the heart, until nearly the 

 entire yolk is covered. This difference between the embryo of the 

 chick and its own extra-embryonic blastoderm or the embryo of 



i The first part appeared in BIOL. BULL., 1903, Vol. V., No. 2 : " Experiments on 

 the Amnion and the Production of Anamniote Embryos." 



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