ORIGIN OF MONSTERS. II 419 



As an other case where the duplication has apparently oc- 

 curred at a late stage (during the formation of the embryonic 

 body) may be regarded the embryo (mesocatadidymus?) presented 

 in figure 13. 



This is a monster to which I attach much significance, be- 

 cause it most strikingly suggests the syngenesis of 'defects' 

 with 'excess.' For its anterior part is highly deformed and 

 defective while the greater part of the trunk and the tail — the 

 former only partly — are duplicated, the spinal cord and noto- 

 chord being multiple. 



Examination of sections shows these conditions in a very 

 convincing manner. 



With the description of the defects of the head we shall not 

 concern ourselves here, as it has a special bearing on the origin 

 and differentiation of the lens and is therefore reserved for 

 another paper. Suffice it to state, however, that the central 

 nervous system is very defective throughout for about the an- 

 terior third of the body, i.e., to about the level of a plane pas- 

 sing transversely through the posterior part of the (only) 

 pectoral fin. Just about from this level onwards posteriorly 

 the spinal cord, in successive transverse sections, is observed at 

 first to flatten and then to spread out more and more from side 

 to side. It gradually increases in size and in many consecutive 

 sections appears to be vacuolated and to exhibit evidence of 

 cytolytic degeneration (fig. 20). The latter now becomes 

 more and more conspicuous with each consecutive section (fig. 

 21), cellular elements disappearing more and more, until in 

 some sections not much more than the framework of supporting 

 tissue is left. The nuclear debris of the chromatolyzed cells 

 can be observed at quite a distance from this degenerated part 

 of the cord. 



This has then, evidently, been the part which suffered the 

 greatest injury from chemical alteration and subsequently 

 presented a point of least resistance to the action of osmotic 

 pressure. For from this level on the spinal cord divides at first 

 into two and then into more parts. The notochord is also 

 multiplied, while in sections at a still more posterior level the 



THE JOURNAL OF EXPERIMENTAL ZOOLOG1 , VOL. 24, NO. 2 



