432 Harris Hawthorne Wilder 



pared a series of embryograph drawings for the construction of a wax 

 modeh The excellent work of Kaestxer upon this very subject will 

 render any work of mine on the same subject superfluous, especially as 

 I have become so much interested in the investigation of later mammalian 

 embryos by the use of the same methods. That such methods, applied 

 to teratology, are quite new is indicated by his confession that he kept 

 his first double embryo for tw^o years in Canada balsam, to serve as a 

 "Schaustiick" before it occurred to him to section it, and here again 

 comes a parallel from the other side of the Atlantic, for my preparations 

 were handed me in precisely this form and I had first to dissolve them 

 out of the balsam before sectioning. 



Aside from the descriptive part there is a little general discussion, 

 although the author feels that we are hardly ready for it as yet. At the 

 outset he states that as yet no "Doppelbildungen" have been experi- 

 mentally produced in the case of Amniotes, although it has been accom- 

 plished in the case of certain Anamnia and invertebrates. The claims 

 of former investigators that they have produced such monsters in arti- 

 ficially treated hens' eggs (by varnish, shaking, high temperature, etc.), 

 cannot be acknowledged, since a fairly large proportion of these nor- 

 mally occurs in eggs, at least those artificially incubated, and it has not 

 been shown that the proportion is any larger in eggs that are specially 

 treated. 



I am, of course, in full accord with this view, and may go still farther 

 and suggest that the double formations produced artificially in Anamnia 

 and invertebrates may perhaps differ essentially from those that are pro- 

 duced by Nature, at least in the ultimate cause. In natural cases it is 

 probable that the cause which is later to produce a double monster lies 

 in the germ-cell previous to the first cleavage, and that the more or less 

 complete loss of continuity between the early blastomeres which undoubt- 

 edly takes place, is the first of the visible results of the germinal condition. 

 This, in its turn, helps to condition the whole later development and 

 when induced artificially, naturally produces similar results. A germinal 

 cause is, however, much more delicate and precise than a mechanical one 

 can be, and thus the results of the latter cause are not as symmetrical 

 and perfect as are those produced by the former. The experiments are 

 of extreme value in suggesting one of the early mechanical steps emplo3^ed 

 by Nature during the genesis of a double monster, but that the ultimate 

 cause lies in merely a separation of the blastomeres does not appear 

 probable. 



