204 The Philippine Journal of Science 



Kaestner shows a similar confluence in a set of his chick 

 twins, but does not show a median vein. Furthermore he 

 considers the confluence in the process of developing into a 

 single heart and concludes that in all probability if growth had 

 continued there would have developed a single heart. The con- 

 fluence of the veins does not correspond to the position of the 

 heart in embryos of this stage of development, but from the 

 single tubular heart that lies more cephalad. If any conclusion 

 can be drawn, one heart should develop from each tubular heart, 

 as this corresponds to the region where it normally develops. 



REFERENCES 



1. Burckhakt, R. Doppelanlage des Primitivstreifens bei einem Hiihnerei. 



Arch. f. Anat. u. Physiol— Anat. Abth. (1888), 431. 



2. Kaestner. Doppelbildung an Vogelkeimscheiben. Ibid. (1902), 117. 



3. Mitchell. On a double chick embryo. Journ. Anat. & Physiol. (1890- 



91), 25, 316. 



4. Reichert. Anatomische Beschreibung dreier, sehr fruhzeitiger Doppel- 



Embryonen von Vogeln, — zur Erlauterung der Entstehung von Doppel- 

 Missgeburten. Arch. f. Anat., Physiol, u. wiss. Med. (1864), 744. 



5. Ruth, E. S. On the development of twins and other polyembryos, 



with especial reference to four sets of duck twins. Phil. Journ. Sri., 

 See. B (1916), 11, 109. 



