8o Translation from Purkinje 



muscular fibers of the mesometria play the most important role as 

 they draw the oviduct hither and thither, bellying, twisting, and con- 

 [^21^ stricting it. At this time the part of the mucous membrane which en- 

 velops the yolk secretes albumen which takes the form of membranes 

 and promptly sticks to the yolk; on the other hand the part before 

 and behind the ovum is constricted and moulds the secreted albu- 

 men into a column, which is twisted upon itself as it is moved along 

 spirally and is gathered up at both poles of the egg; as a result of this 

 tQrsion it is in general drawn toward the root by which it is attached 

 to the yolk, and there it merges into the rest of the albumen (fig. 24). 

 Since the chalazae are inserted on the ends of the axis of the yolk, 

 their purpose seems to be chiefly to keep the axis rotating always in a 

 single plane. So it comes about that the cicatricula is always the 

 uppermost part of the yolk and nearest the heat of the incubating hen. 

 If you rapidly twirl an egg in a mechanical device, the chalazae do 

 not acquire more convolutions but the twisted ligamentum albumenis 

 is torn from the shell. 



§ 19 



Concerning the formation of the 



shell membrane. 



The shell membrane begins to be laid down on the external sur- 

 face of the albumen in the lowermost part of the oviduct, which lies 

 between its isthmus and the uterus. First the sharper end enters and 

 is invested with [shell] membrane so that at the blunter end the al- 

 bumen may often be seen still bare. The isthmus region is so stretched 

 in this period of activity that the folds of the lining membrane are 

 completely wiped out and there is very great tension in this distinctly 

 narrower part of the oviduct. Perhaps the greater irritation of the 

 membrane elicits a denser secretion which produces the membrane. 

 The brief interruption of the mucous folds at the level of the isthmus 

 constriction should also be noted. At this point the transition between 

 the albuminous and membrane secretion is made, and here perhaps 

 the conditions are provided for the formation of the ligamentum 

 alhuminis at the sharper end of the egg. The shell membrane is laid 

 down double; the inner is composed of straight fibers of microscopic 

 dimensions, the outer presents no distinctive structure* (fig. 25). 



* In the egg of Coluber Natrix this internal layer consists of the most beautiful 

 wavy fibers. See G. R. u. L. Ch. Treviranus: Verm[ischte] Schriften [Anatomischen 

 und Physiologischen Inhalts (Gottingen: 1816-21).] Vol. 1, p. 142. [The particular 

 essay referred to is by Gottfried Treviranus (1776-1837): "Ueber die organische 

 Elemente des thierischen Korpers." The description and figure refer simply to 

 "Eierschale" so that the observations on Coluber were Purkinje's own.] 



