ORIGIN OF MONSTERS. II 415 



separation of blastomeres, but also how such monsters may 

 come about through dissociation at a later stage (up to the 

 time of gastrulation) as in the experiments of Spemann ('00- 

 '04) where such dissociation was effected by mechanical con- 

 striction along the potential embryo's longitudinal axis. It is 

 only necessary to imagine that a chemical lesion of a moderate 

 degree is sustained more or less along the germ's chief axis. 

 Along this chemically altered area a rupture may take place 

 owing to least resistance to osmotic pressure. Depending upon 

 the extent of this passive 'fission/ a diprosopos, dicephalos 

 or any diplopagus may result from the further development of 

 the, thus partially, doubled primordium. The assumption of 

 this chemical action, made already by Bataillon (I.e.), 14 does 

 not necessarily apply to all duplicities of 'Nature' and not even 

 to all double embryos in teleosts, for as I have already men- 

 tioned, the duplication of the embryonic anlage at any stage 

 before the conclusion of gastrulation might be accomplished by 

 the physical action of osmotic pressure only. And even the 

 malformations of the components of the resulting duplicities 

 might well be due to this factor alone. 15 



In my experiments, however, substances have been added 

 to the sea water which, owing to their chemical properties are 

 toxic (i.e., injurious to the most important life processes), 

 and which also, owing to their molecular weights have changed 

 the tonicity of the sea-water. It is therefore not surprising 



14 Bataillon (I.e.) also assumes that in his experiments chemical alteration 

 may have played a considerable part in the genesis of defects. 



15 As an example I am inclined to regard the frequently observed Salmonid 

 double monsters. In a considerable number of trout double embryos in my 

 possession (collected in a fish hatchery in the vicinity of Freiburg i. B.) exam- 

 ination of sections fails to disclose anything that would suggest chemical alter- 

 ation as underlying the duplication of the germ and the accompanying deformi- 

 ties of the resulting double embryos. The nature of the alteration of the water 

 in which these embryos have developed is, of course, unknown and the factors 

 responsible for their developmental anomalies are, undoubtedly, left alto- 

 gether to speculation. It seems not improbable, however, that in such cases 

 the osmotic pressure of the water may be increased by the presence in it of 

 some (otherwise perhaps not injurious) metallic salts, or possibly blastotomy 

 here results from increased temperature or "old age" of the eggs (cf. pp. 

 319-321 and 327). 



