III. 5 HEAT 109 



H. DRIESCH. Entwicklungsmech. Stud. VII : Exogastrula unct Anen- 

 teria, Mitth. ZooL Stat. Neapel, xi, 1895. 



C. L. EDWARDS. The physiological zero and the index of develop- 

 ment for the egg of the domestic fowl, Gallus domesticus, Amer. Jown. 

 Phys. vi, 1901-2. 



A. W. GREELEY. On the effect of variations in the temperature upon 

 the process of artificial parthenogenesis, Biol. Bull, iv, 1903. 



0. HERTWIG. Ueber den Einfluss verschiedener Temperaturen auf 

 die Entwicklung der Froscheier, S.-B. konig. preuss. Akad. Wiss. Berlin, 

 1896. 



0. HERTWIQ. Ueber den Einfluss der Temperatur auf die Entwicklung 

 von Ranafusca und esculenta, Arch. mikr. Anat. li, 1898. 



S. KAESTNER. Ueber kiinstliche Killteruhe von Hiihnereiern im Verlauf 

 der Bebriitung, Arch. Anat. Phys. (Anat.}, 1895. 



S. KAESTNER. Ueber die Unterbrechung der Bebriitung von Hiihner- 

 eiern als Methode zur Erzeugung von Missbildungen, Verh. Anat. Gesellsch., 

 1896. 



F. R. LILLIE and E. P. KNOWLTON. On the effect of temperature on 

 the development of animals, Zool. Bull, i, 1898. 



L. SALA. Experimentelle Untersuchung iiber die Reifung und Be- 

 fruchtung der Eier bei Ascaris megalocephala, Arch. mikr. Anat. xliv, 1895. 



0. SCHULZE. Ueber die Einwirkung niederer Temperatur auf die 

 Entwickelung des Frosches, I, Anat. Anz. x, 1895. 



0. SCHULZE. Ueber die Einwirkung niederer Temperatur auf die 

 Entwickelung des Frosches, II, Anat. Anz. xvi, 1899. 



6. ATMOSPHERIC PRESSURE. THE RESPIRATION 

 OP THE EMBRYO 



The respiratory exchange, which is so characteristic a function 

 of adult organisms, is a necessity for the embryo also, and in 

 some cases can be detected in very early stages indeed. 



In the case of the Chick this need of oxygen is shown by the 

 arrest or distortion of development, or the death of the embryo 

 when the egg is placed in too confined a space, or when the 

 shell is varnished, wholly or above only (Mitrophanow, Fere"), 

 though a coat of varnish on the lower side has no effect accord- 

 ing to the latter author ; or again, when the egg is placed in an 

 atmosphere of hydrogen, or when the pressure of the ordinary 

 atmosphere is reduced (Giacomini). 



Giacomini found that at a pressure of about 600 mm. the 



