The Morphology of Cosmobia 393 



the perfect or the imperfect side, and thus belong to both components. 

 In 'No. Ill, where there is no aortic arch on the imperfect side, the two 

 carotids of that side arise directly from the left ventricle, but an anas- 

 tomosis between the left carotid and the pulmonary arch is perhaps a 

 ductus Botalli, and suggests that morphologically this apparent left 

 carotid includes as well a rudimentary aortic arch. 



This comparison of the circulatory system of several monsters of the 

 same type is suggestive of a series of secondary modifications of a pri- 

 mary symmetrical plan exhibited by each at an earlier period. What 

 this original plan may have been in the case of his own specimen is 

 figured by Mayor^ side by side with his instructive diagram of the exist- 

 ing relations (the equivalent of my No. III.) In this diagram Mayor 

 suggests, as I have done, an earlier persistence of both the pulmonary 

 and aortic arches of each compound heart, forming a circle, broken at 

 two opposite points by the hearts of the perfect and imperfect sides, and 

 at points 90° from this by the two aortas, each of which is thus formed 

 by the union of the pulmonary and aortic arches of the two adjacent 

 half -hearts; i. e., the two arches belong primarily to that individual 

 whose aorta they form. This ideal arrangement is, however, not borne 

 out by Mayor's own specimen (No. Ill), even with the replacement of 

 the aortic arch of the imperfect side, since here (and in the majority of 

 the cases) the arches cross over each other and supply, not the compo- 

 nent to which their ventricle of origin belongs, but the opposite side. 

 Serious discussion, however, concerning the exact form of the primary 

 relation of these parts is, in the absence of definite data, hardly worth 

 while ; we may well wait until the lucky find of an early embryo of this 

 type of monster gives us exact knowledge on this point. The important 

 point to assert is that evidently there is primary symmetry in the organs 

 of circulation as well as in other less active parts, that in the early em- 

 bryonic stages they exhibit this primary symmetry, and that during later 

 development they become modified in accordance with their physiological 

 needs. 



Part II. Double Eyes. 



General Principle. By a "double eye" is here meant a bilaterally 

 symmetrical eyeball formed of two components. Such double eyes occur 

 among Cosmobia in three different ways, as follows : — 



Type 1. In a Cyclops; in this form the two eye components are the 

 right and left ones of a single individual. 



