The Morphology of Cosmobia 435 



defective half develops "auf derjenigen ITalfte des Keims, von welcher 

 das Vorderende der Hauptsymmetrieebene abgewandt ist." This result 

 he attributes to the definite loss through this procedure of the anlagen 

 of certain median parts, which consequently never even begin to develop, 

 and thus the parts lateral to these develop in contact from the start. 

 This explanation is quite a different thing from a "fusion," although 

 the results are similar, as indeed they are. The different degrees of 

 cyclopy which he obtains, and which can be arranged in a natural series 

 "die vom normalen Zustand durch Uebergange zum hochsten Grad des 

 Defects fiihrt," thus receive a natural explanation as due to a varying 

 amoimt of these Anlagen cut off by the ligature. With this basis for 

 the explanation of cyclopy he naturally rejects the older hypothesis of 

 Dareste, that cyclopy is induced by a premature closing of the medul- 

 lary tube, and points out the fact that we cannot know whether the 

 cyclopy is caused by this premature closing, or whether the premature 

 closing is the result (perhaps the earliest that is visible to the observer), 

 of a cyclopic condition of the germ. In the medullary tube of an 

 anterior half that afterwards develops cyclopy there is less material than 

 in a normal one, and it would therefore naturally close earlier, since 

 it has less material to control. 



The monsters produced by Spemann are hard to classify, and are 

 occasionally quite unlike those thus far known to develop in nature. 

 They seem never to be Jani, of either the symmetrical or unsymmetrical 

 types, although he calls them such, for a Janus must have two bodies 

 placed opposite each other, suggesting the true composition of the faces, 

 and the Spemann monsters are always single bodied, with a more or 

 less doubled head and suggest rather the various grades of dicephaly, 

 like my Terata I and XII. He figures one absolutely unique case (1. c. 

 Taf. 24, Figs. 1-6 and Text-figures W, X and Y), in which there are 

 four eye components, symmetrically placed, and all united into a single 

 piece or complex, which the author, and creator, calls "das grosse Vierer- 

 auge." From the figures, both of the entire monster and of several 

 sections, it passes all the criteria of a typical cosmobion, and the sections 

 are as S3'mmetrical, and as free from all suggestion of the pathological, 

 as are those of the series of my Teras I. 



The author finally discusses the relation between artificially produced 

 monsters and those that arise spontaneously in a state of nature, and 

 states it as his belief that it is yet too early to herald such results as his 

 as the definite explanation of monsters of the spontaneous class, although 



