100 MR. NOEL TAYLER OX A UNIQUE CASE OF 



It may here be noted that this blastorlerm would seem to 

 fit in well with C. M. Child's theories of development and 

 i-epi-oduction by the physiologica] isolation of parts (1). 

 4. It has been pointed out abore that the primary nature of the 

 abnormality of the two rudiments is a lack or deficiency, 

 and it would seem that this deficiency must be regarded as 

 reciprocal. While the posterior parts of Rudiment n are 

 quite norma!, the amount of disturbance increases as we 

 pass anteriorly. !From section A of the discussion it was 

 concluded that the seat of the pi-imary disturbance was the 

 extreme anterior region of the embryo, in particular of the 

 medullary plate. The inference seems fairly natural that 

 Rudiment /? represents that portion of the geiminal substance 

 which was lacking in the extx-eme anterior portion of Rudi- 

 ment a. Expressed in terms of Child's theories, one would 

 say that that portion of the germ from which Rudiment /3 

 developed came to lie outside the range of dominance of the 

 primary centre, and thus becoming physiologically isolated, 

 commenced to develop as an independent centre. Accox^ling 

 to Child (1), " Parts of the individual may come to lie 

 beyond the range of dominance in consequence of increase 

 in size of the whole, of decrease in range and degree of 

 dominance by decrease in the metabolic rate in the dominant 

 legion, of decrease in conductivity of the paths of correla- 

 tion, and of the direct local action of external factors which 

 increase the independence of subordinate parts." The factors 

 responsible for the initiation of the secondary centre of 

 eanbryo formation on blastoderm E must presumably have 

 been somewhat of the nature of the second and fourth of 

 these, or of a combination of the two. The more likely 

 explanation would seem to be that the primary disturbance 

 involving the anterior medullary plate region, or more 

 strictly (since it must have occurred at a very early period) 

 the apical region of the major axis, led to the defective 

 development of the anterior portion of the central nervous 

 system, with the secondary modifications of Rudiment a 

 discussed in Part A above. On the other hand, the abnormal 

 development of the anterior end of Rudiment a would have 

 been accompanied by a decrease of " metabolic rate," and 

 Ivence in the range of dominance with the consequent 

 isolation of Rudiment /3 as a secondary germinal centre. 

 5. While, as emphasized in 3 supra, the two rudiments clearly 

 lie on a single long axis, it will be noticed that this axis 

 curves somewhat to the left in the region of Rudiment ft. 

 It seems possible that this fact may be correlated with 

 the morphological asymmetiy of the head of Rudiment n, 

 which is more defective on the right side (see Pis. II. & III. 

 tiys. 3, 4, E 3 and E 4). These two facts suggest an obliquity 

 ivf the ori-giixil disturbance iu relation to the major axis. 



