334 GEORGE W. BARTELMEZ. 



The Oviducal Orientation. We have seen that one end of the 

 principal axis may differ from the other in regard to the shape 

 and pigmentation of the shell, the position of the air space, the 

 ligamentum albumenis, in the size and character of the chalazae, 

 and the relation of the egg to the oviduct. The vital link in the 

 evidence for the thesis that the principal axis is an expression of 

 an ovarian axis of symmetry was obtained when it was found 

 that the end of the long axis of the yolk which is to pass first 

 down the oviduct is predetermined in the ovary (Bartelmez, 

 1912, p. 292 ss). In the pigeon at least, the latebra of Purkinje 

 is, like the blastodisc, lighter than the mass of yellow yolk. 

 Purkinje (1830, p. 7) believed the converse for he was much 

 struck by the resemblance of his "fluid-filled cavity" to a plum- 

 met and did not make any tests. He did know however that 

 the contents of the latebra have the same histological structure 

 as the white yolk about the blastodisc. His figure (Tab. I., 

 Fig. 1 6) of a median section of the yolk of a hen's egg shows the 

 center of the latebra nearer the animal pole than the vegetal. 

 This is still more marked in the pigeon's egg (see Bartelmez, 

 1912, figs. 38 and 39). This specifically lighter latebra is nearer 

 one end of the long axis than the other end and so one end of the 

 ovum gravitates toward the cloaca and is received first into the 

 oviduct as was described in my 1912 paper. It is worth noting 

 that in three clearly objective drawings in the literature the 

 latebra is shown nearer one end of the long axis of the hen's 

 ovum; they are v. Baer's Figs, i and 2, Plate III. (1828) and 

 Duval's Fig. 21 (1889). This observation can be made with 

 certainty only on oocytes during the final growth period or shortly 

 after ovulation. Eggs taken subsequently show more or less 

 diffusion between latebra and surrounding yolk so that accurate 

 measurements are usually impossible (cf. my figures just men- 

 tioned). Purkinje made mention of this fact in 1825. It will 

 be remembered in this connection that the yolk increases in 

 weight as it passes down the oviduct, taking up water from the 

 surrounding albumen during its progess (cf. Curtis, 1911). 



Since I was able to show that the position of the latebra 

 nearer one end of the long axis is determined by the corresponding 

 position of the germinal vesicle in earlier stages it is possible 

 to trace the principal axis with one end morphologically different 



