The Morphology of Cosmobia 395 



there are involved tM-o head components from which the eye components 

 have been derived. In cases in which the two eyeballs are distinct and 

 possess a short interval between them (and these cases also should be 

 included in the study of double eyes), the two external recti, or a single 

 bilateral muscle to represent them both, may be expected in the interval 

 between them, while the internal recti will be found upon the apparent 

 outer sides, thus corroborating the fact of the reversed position of such 

 components. 



Furthermore it will be noticed that Types 1 and 3, placed in series, 

 with the condition found in normal individuals interposed between them, 

 correspond exactly with the series shown in Fig. 1, as may be seen 

 by a comparison of this diagram with the accompanying Fig.20, although 

 no attempt has been made to make the individual stages correspond. 

 This last diagram represents the eyes of the former series, and shows 

 them as if the heads were cut in cross-section at the level of the eyes, 

 and the investigator were looking down upon the cut surface. Of the 

 stages represented, Nos. I-VI are cyclopean, VII and VIII show the 

 different degrees of eye separation in a normial individual, and the 

 remaining stages, IX to XIV, form the series leading to dicephaly. 

 These latter thus represent the cases designated here as Type 3, and the 

 cyclopean stages, I and VI, Type 1. 



The study of these three types of double eyes, aside from their differ- 

 ences in the relationship of the eyeball elements and in the number of 

 component individuals involved, possesses another distinct advantage in 

 the present connection, that of being a passive system, without function 

 during embryonic life, and hence not subject to the secondary mal- 

 formations due to functional activity under abnormal conditions, as in 

 the case of the circulatory system. Allowing for possible mechanical 

 hindrances, due mainly to insufficient room for complete development, 

 and which become more manifest as development proceeds, these parts 

 ought to show with especial clearness the characteristics of typical 

 cosmobia, perfect bilateral symmetry and normal tissues. Owing to this 

 importance in point of theory I have thought best to publish all the cases 

 that have come to my hand. These represent all three of the types and 

 are as follows: — 



Of the first type I have two specimens, Terata VI and VII, the one a 

 Cyclops child at term, the other an advanced pig fetus. Type 2 is 

 represented by the double eye of the imperfect side of the Baldwin 

 Synote, situated just above the double ear described above, and for Type 



