174 BLASTOGENIC VARIATIONS. 



the effects of placing fowls' eggs vertically instead of 

 horizontally during development, of keeping them 

 slightly above or below the normal temperature of incu- 

 bation, of heating different parts of the egg unequally, 

 and of modifying the conditions of respiration by var- 

 nishing part of the shell.* Various considerable mal- 

 formations were produced, but these were more or less 

 the same, whatever the conditions that produced them. 

 Professor Windle,t who has extended these investiga- 

 tions and determined the effects of various other 

 agencies, as electricity and niagnetism ? on development, 

 came to a similar conclusion. He considered that these 

 disturbing agents act, in the majority of cases, on that 

 part of the developing organisation which is concerned 

 with the formation of the vascular system of the em- 

 bryo, and so indirectly produce the malformations ob- 

 served. 



The suggested connection between considerable mal- 

 formations and sports has not as yet been borne out by 

 Dareste's researches, although observations have been 

 made with the object of finding it. In these observa- 

 tions the conditions found to produce considerable mal- 

 formations were reduced in strength, in the hope of 

 thereby obtaining only slight anomalies, compatible 

 with continued existence and the procreation of off- 

 spring. Unfortunately the domestic fowl, which was 

 invariably made use of, is unsuitable for such observa- 

 tions. The type is so diversified that the experimenter 

 who obtains some variety can never be certain whether 



* " Reclierches sur la Production artificielle des Monstrosites," 

 Paris, 1877; second edition, 1891. 

 fProc. Birmingham Phil. Soc., vii. p. 220, 1890. 



