56 E. I. WERBER. 



Twins were found only in a few cases and only once were true 

 "Siamese" twins observed. They were much deformed, had 

 one common heart and only vestigial eyes. Several eggs were 

 recorded, in which an anterior duplicity had developed. In one 

 of these latter cases the components of the duplicity were totally 

 blind, hydrocephalic, their hearts were very delicate, the blood 

 vessels rudimentary and the yolk-sac was covered with dense 

 networks of richly pigmented blood islands. 



These monstrous embryos hatch only very rarely, most of 

 them dying after the development has reached the stage in which 

 the remant of the yolk-sac is in the normal embryo converted into 

 the anterior body wall. As far as could be determined from the 

 embryos in toto it is the enormously large (oedematous?) peri- 

 cardia that mechanically obstruct the formation of the ventral 

 body wall. The correctness of this interpretation will be tested 

 by microscopic sections of these embryos. 



The mechanism of the formation of the described monsters can 

 at this time not even be definitely suggested. The observation 

 was made that the yolk-sac in all extremely malformed embryos 

 shows a marked decrease in size as compared with that of normal 

 eggs of the corresponding stage of development. The greater 

 the degree of injury inflicted on the embryo the smaller the yolk- 

 sac. It is not impossible that the chemicals used in these experi- 

 ments indirectly bring about this decrease in the size of the 

 yolk-sac. For it was noticed that the chemicals used in these 

 experiments softened the egg-membrane considerably, a fact 

 which suggests an increase in the permeability of the egg. 

 Owing to both increased permeability of the germ-disc cells and 

 to internal osmotic pressure of the yolk-sac, an escape of sub- 

 stance from the yolk-sac might have been caused, which, being 

 forced out at different points of the yolk-sac, might have frag- 

 mented the germ-disc. Many eggs were observed in which 

 this fragmentation of the germ-disc was very evident. Some 

 parts of this ruptured germ-disc may be so badly damaged as 

 not to be able to develop further, while the remaining fragments, 

 even if they are very small, may still give rise to various monsters, 

 hemiembryos, dwarfs or even to a solitary eye. Or possibly the 

 decrease in size of the yolk-sac of malformed ova may point to 



