Arteries in Monsters of the Dicephalus Group 



469 



Summary. 



Four cosmobia have been studied and general comparisons made. 

 Of three of them the heart and anterior arteries have been made the sub- 

 ject of special investigation. The study has demonstrated : — 



(1) That primarily each Teras has developed in an orderly, symmetri- 

 cal manner in accordance with the laws of growth inherent within it. 



(2) That as the structural parts of the components diverge, the arteries 

 in the region involved reflect the deviation part for part, and the mor« 

 posteriorly the divergence passes the more the heart becomes involved. 



(3) That the divergence of all the parts involved is perfectly uniform 

 and symmetrical. 



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V 



Text Fig. 5. Diagram showing the transformations in the primitive 

 arterial arches in Teras XX. 



(4) That in each case it has been possible to refer the vascular arrange- 

 ment back to an embryonic condition known in normal organisms by 

 considering this latter condition as modified through various degrees 

 of doubling. This has been done by reducing the teratological condi- 

 tions to diagrams. 



(5) That it should be emphasized that in explaining these cases 

 they must be considered double to a definite extent from their beginning, 



