The Morpliology of Cosmobia 373 



there results a pair of free components, in short, duplicate twins ! Dur- 

 ing early embryonal life, when there is no clear distinction between 

 embryonal and extra-embryonal parts, it would be without question 

 a Diplopage, but the subsequent abandonment of those parts in which 

 the union occurs leaves the two comporients free from each other, a 

 ditference of no moment to the morphologist but a most vital one from 

 the standpoint of the individuals concerned. 



As the terms that have been applied to the various stages of this 

 series are numerous and varied, I have hoped to simplify matters a little 

 by suggesting a series of terms, the most of which are already in use, 

 which designate the condition in the simplest way; namely, using in 

 each case the Greek term for the point at which the union begins ante- 

 riorly, joining to this the usual term for a monster with two components, 

 — pagiis, (-n-qytvixL) . The term omphalo- is often added to the compound, 

 as "Thoraco-omphalopagus," but this is hardly necessary as the um- 

 bilicus must of necessity always form the posterior limit of such mon- 

 sters. We have thus the terms, Cephalopagiis, Gnatlwpagus, etc., as 

 given in the diagram, a set of terms which may be freely added to if 

 we wish to express grades between those given. 



2. Variations in the amount of lateral torsion of the two compo- 

 nents; with involution of certain of the parts upon the less favored side. 

 It rarely happens that the components so exactly face each other in the 

 head region that the two resulting compound lateral faces are perfectly 

 equal. Such a case is called a "Janus symmetros" and is one of the 

 greatest teratological rarities. Usually in this region there is what may 

 be termed a lateral torsion, with the result that the compound face upon 

 one side is complete while that upon the other suffers a greater or less 

 involution, that affects the median parts at least, but, with a greater 

 degree of involution gradually affects parts that are more laterally placed. 

 The series formed by this principle is shown in diagrammatic form in 

 Fig. 3, which begins with a Janus symmetros and ends with so complete 

 a degree of involution that the external features of the face are entirely 

 suppressed upon the imperfect side, giving the compound head the 

 external appearance of a single one, facing in a direction that is really 

 lateral in respect to the actual position of the components. This ex- 

 treme condition is that realized by my Teras XIY, a pig with eight legs, 

 two bodies, and apparently a single head placed sideways with respect 

 to the bodies. In all cases the torsion is most pronounced anteriorly 

 and becomes gradually less towards the umbilicus, at which point it 

 disappears and the two bodies are opposite each other. 



