394 Harris Hawthorne Wilder 



Type 2. In an Iniops or Synote, i. e., on the imperfect side of a Janus 

 monster; in this form the two eye components are those of different 

 individuals, the right of one and the left of the other. 



Type 3. In an incomplete Diprosopus, in which the two head com- 

 ponents are distinct about as far as the eye region, bringing the 

 two inner eyes of the two components into close contact, or so as to 

 form a compound organ. 



As for the relative position of the two eyes in the different types, the 

 components involved are always a right and a left. In types 1 and 2 

 they are normally related to each other, that is, the right and left com- 

 ponents are placed on their respective sides, but in type 3, they ore 

 reversed so that the anatomically right eye is placed on the left and vice 

 versa. This follows in each case from the relation of the components 

 to each other, and may be easily proven by a study of the structure, the 

 best guides to the original position of the eye components being the 

 Trochlearis and Abducens nerves, through which a component, although 

 much reduced, may be definitely oriented. 



The relation of the eye components in Type 1 is the normal one for 

 the two eyes of a single individual. The median eyeball is strictly 

 bilateral and its lateral aspects are like those of separate eyeballs fur- 

 nished with normal external recti. In cases in which the two components 

 are very deficient, the internal recti may be entirely wanting, although 

 the typical parts generally manage to appear by means of certain dis- 

 placements and accommodations. 



Type 2 is the most anomalous of the three, but may be easily under- 

 stood by a glance at the diagram that shows different degrees of torsion 

 in monsters of the Janus type, especially stages III and IV. [Fig. 3, 

 p. 374.] Here again the relation is normal so far as the eyes themselves 

 are concerned, but the two components belong, not to a single individual, 

 but to two, the left eye of component A being fused with the right one 

 of component B. In spite, however, of this radical difference between 

 Cases 1 and 2, the results are extremely similar, and so far as I have had 

 opportunity to judge, the stages in the reduction of one parallel the cases 

 in the other, so that from the study of the eye alone, without tracing 

 out the cranial nerves to their origin it would be difficult or even impos- 

 sible to say from which type a given double eyeball had been taken. 



Type 3 is, in the position of the components, the exact opposite of the 

 first two, for here the sides of the two eyeball components that are in 

 contact with each other are the anatomically outer ones. As in Type 2 



