532 



canal and a series of paired somites numbering 21 in the one case 

 and 19 in the other. The latter was in a contorted condition being 

 bent upon itself in two right angles and this one also contained a curious 

 bladder like dilatation of the mid brain vesicle. Each chick had a 

 separate heart into which paired omphalo-mesenteric veins opened, the 

 inner of each pair being small and soon confused with its fellow. The 

 heart of the twisted embryo had been displaced so that it came to lie 

 underneath and to the right side projecting a little beyond the fore brain 



F. B. 



H. » 



D. 



A. p. 



Figure 2. Photograph of Specimen B. 

 brain vesicle. Other letters as before. 



D Abnormal dilatation of mid 



and thus until it was cleared it gave the appearance of only one heart 

 (see fig. 2). The region of fusion was right at the anterior end 

 where the two fore brains had run together into a somewhat con- 

 fused mass in which the optic vesicles could not readily be made out 

 although further back the auditory pits were easily distinguishable in 

 both cases. In front of the head was the amniotic fold, a structure 

 obviously of double origin and indeed the whole blastoderm especially 

 the sinus terminalis showed this duplicity. 



