ORIGIN OF MONSTERS. II 423 



On following the sections further the brain of the larger com- 

 ponent is observed to increase to a very large size (figs. 26 and 

 27). Cellular areas predominate in it and are strangely in- 

 termingled with fibrous areas. It is difficult to escape the im- 

 pression that distortions of this nature can have resulted from 

 anything but a disorganization of parts of the primordium and 

 subsequent processes of regulation. 



At this level there can be observed in the larger component 

 also a very small, vestigial ear vesicle (figs. 26 and 27). More 

 posteriorly the notochord of this component is doubled, thus 

 indicating dissociation of its anlage at an earlier stage of de- 

 velopment. The (rudimentary) tail of this component comes 

 into view in the last sections. A rudimentary tail is also ob- 

 served in sections passing through the last part of the smaller 

 component (fig. 27). 



The internal organs of both components are almost entirely 

 obliterated. 



A point of interest is presented also by the epidermis of both 

 components on the side on which they are conjoined. A cluster 

 of large cells (d.e. figs. 25, 26 and 27) is noted here to come off 

 directly from the epidermis. The large size of the cells would 

 seem to indicate that having through dissociation lost their cor- 

 relation with the epithelium of which they originally formed a 

 part, there was no restriction to their expansive growth. In 

 some sections the nuclei of these cells exhibit evidence of chro- 

 matolysis, thus suggesting that chemical alteration may have 

 partly been responsible for dissociation (chemical blastolysis) . 



Turning, now, to the morphogenesis of this monster, we are 

 justified, I believe, in assuming that it is a product of the com- 

 bined action of, both osmotic and chemical, blastolysis. The 

 former ('blastotomy') may by separating blastomeres (of the 

 two-celled stage) have severed their mutual correlation, thus 

 allowing each to develop independently. In the course of 

 further development, however, the two, apparently not widely 

 separated, embryonic primordia came into contact along their 

 lateral surfaces where they coalesced. 



