ORIGIN OF MONSTERS 555 



observed to gradually assume a shape approaching the normal. 

 At this level one of the ear vesicles has disappeared from view 

 while that of the other side (a very large one) is very prominent 

 in the section. Laterally and ventrally from this ear vesicle 

 (fig. 62) is seen a rudimentary optic cup. In the last sections 

 the spinal cord runs across between the two parts of the embryo. 

 It is particularly in these sections that the true nature of the 

 monster is disclosed. From them we see that the posterior half 

 of the embryo's body is in relation to the embryo's longitudinal 

 axis turned at an angle of almost 180°. An oedematous blasto- 

 dermic cavity filled with plasma and extending between the two 

 so disarranged parts of the embryo has given the latter the ap- 

 pearance in toto of coalesced very malformed twins. 



What is, now, the probable morphogenesis of this monster? 

 The presence of one eye only would, according to what has been 

 stated in the preceding, point to blastolytic injury sustained by 

 the early embryonic primordium. This injury seems to be evi- 

 denced by the following facts. The ophthalmoblastic material 

 of one side has, owing to chemical alteration, been somewhat 

 inhibited in development and has given rise to an imperfect eye. 

 The ophthalmoblastic cells of the other side have suffered great 

 destruction (owing to increased osmotic pressure after chemical 

 alteration?) and a remnant of them has been fragmented into 

 two parts. Of the latter one has made some initial steps in 

 development (having attained the shape and to some degree 

 the structure of an optic cup) and stimulated the development 

 of a lens, while the other fragment has been dislocated and 

 developed into a rudimentary optic cup at the posterior level 

 of the ear vesicles. The latter are both deformed and oede- 

 matous. The deformities of the brain are such as to point to 

 a hap-hazard regulation of a brain primordium after blastolytic 

 lesion. The oedematous blastodermic cavity filled with plasma 

 suggests that no continuous blood circulation existed, the failure 

 of blood vessels to develop being due to chemical alteration — 

 a condition which can be found nearly always in embryos wliich 

 have sustained blastolytic injury of a high degree. The strange 

 space relation of the posterior half of the body to the anterior 

 would apparently indicate the action of osmotic pressure, which 



