Experiments on Trout Eggs 21 



The deuterogenetic area includes : 



Hindbrain, spinal cord, renal organs, muscles of the trunk, 

 and the whole tail ; but probably not much of the gut except 

 the rectum and anus. 



The accompanying Fig. 11 will show the kind of evidence 

 obtained by the method of using bristles as a means of marking 

 regions on the egg. It is difficult to obtain the exact boundary 

 between the influence of the two activities, because bristles 

 cannot be placed nearer to the lip of the blastopore than about 

 0-5 mm. without causing serious malformations. The bristles 

 were actually placed round the region of Brachet's blastopore 

 virtuel (see pp. 25, 26). 



Experimental Evidence as to Concrescence. 



The first to test this theory by experiment was Kastschenko, 

 who in 1888 operated upon the embryos of an Elasmobranch. 

 He destroyed one part of the rim and found that such destruction 

 did not prevent the formation of the main axis of the embryo. 



The most complete investigation that has been made is that 

 of F. Kopsch who performed a large number of experiments upon 

 the developing embryo of the trout. I give here some figures 

 showing the nature of the operation and the results. 



In Fig. 12 A the mark op represents in A the point in the rim 

 of the disc i.e. lip of the blastopore, at which an injury was 

 effected. Fig. 12 B shows the position of the injury at a later 

 stage when the embryo had eight or nine pairs of protovertebrae. 



According to the concrescence theory, the germinal disc rim 

 growing round should have coalesced with the corresponding part 

 on the other side, and formed the mid-dorsal part of the embryo, 

 namely the neural tube, notochord, and, perhaps the proto- 

 vertebrae. But, as the examination of sections taken through 

 B b showed, the formation of these parts is quite normal, and 

 the injury lies far to the side in the region of the latero- ventral 

 part of the future body wall. The injury has brought about a 

 failure on the part of the rim to progress over the yolk, and a 

 corresponding defect at the side which is just what one would 

 expect if the embryo is formed in the way described. 



Fig. 12 C is a figure of a slightly more advanced embryo 



