PRINCIPAL AXIS OF SYMMETRY IN THE BIRD'S EGG. 327 



The development of the chalazse was first described by Du- 

 trochet (1818-19). His work was confirmed and extended by 

 Purkinje (1825), v. Baer (1828 and 37) and Berthold (1829) 

 among others. The albumen which at first surrounds the newly 

 escaped ovum forms a thin but dense layer over its surface. 

 This albumen is probably secreted according to Curtis (1915) 

 in the infundibulum and neck of the duct. It coagulates into 

 the membrana chalazifera Dutrocheti and is shortly so firmly 

 united with the vitelline membrane that they cannot be sepa- 

 rated. "The tendency, says v. Baer, of albumens in contact 

 with solids to coagulate is well known." The chalaziferous 

 membrane is directly continuous with strands of albumen 

 which were secreted into the lumen of the oviduct above and 

 below the ovum. These strands, attached as they are to the 

 ovum, become the chalazse. According to Coste (1847, p. 291) 

 the ovum is not free to orient itself with reference to gravity 

 until a fluid layer forms between the chalaziferous albumen and 

 the inner dense albumen probably during the period of shell 

 formation in the "uterus." This might happen while the thin 

 solution of albumen is passing through the developing shell as 

 described by Pearl and Curtis (1912). While in the uterus the 

 egg is constantly being turned on its long axis and the ovum is 

 constantly tending to orient itself with reference to gravity since 

 the animal pole is specifically lighter than the vegetal. Conse- 

 quently the chalazal strands attached to the yolk become twisted 

 in opposite directions and as a result there is a partial coagulation 

 of the chalazal albumen resulting in the "hailstones." 



The stage at which the yolk is first free to rotate independently 

 of the surrounding thick albumen and the time when the chalazae 

 as such become visible have not been satisfactorily determined. 

 The nature of the space, too, between the chalaziferous albumen 

 and the inner albumen which makes the rotation possible is 

 most obscure. The suggestion of Taschenberg (1885), that the 

 twisting of the chalazae takes place before the egg enters the uterus 

 is highly improbable. Not infrequently in the hen and pigeon 

 at least, there is more chalazal albumen below the ovum than 

 above it as Purkinje first noted (1825) and consequently the 

 cloacal chalaza is larger than the other. This condition may play 



