128 ISABELLA M. DRUMMOND. 



lie more dorsally. The commissure tlins comes to lie obliquely 

 quite independently of any direct connection with the torsion 

 of the body, and this irregularity is accentuated by a tendency 

 on the part of the commissure to pass even more over to the 

 left side of the body, and so place itself symmetrically with 

 regard to the asymmetrical mantle cavity; or, in other words, 

 symmetrically between its two extreme points of origin. This 

 accessory twist may, therefore, be left out of account for the 

 present purpose, and we are justified in saying that, as far as 

 true torsion is concerned, the connectives only show a twist 

 of 180°. 



The second point to be noticed is that, whereas growth in 

 the circumference of the visceral hump has been hitherto so 

 slow as to be almost inconsiderable — for instance, between 

 Stages D and G — though at the same time torsion has 

 advanced rapidly, an enormous growth has taken place 

 between Stages G and H. I believe that it is in these two 

 facts that we find the solution of the difficulty. Between 

 Stages G and H a kind of accessory or false torsion has taken 

 place among the organs in the posterior region of the visceral 

 hump, due merely to unequal growth amongst themselves, 

 and not having as its concomitant further true torsion in the 

 anterior region. If we seek further for the cause, I think we 

 iind it in the lengthening of the alimentary canal, and the 

 great development of the stomach, which have together 

 brought about the present relation between the stomach and 

 liver, and also in the sudden rapid widening of the original 

 left portion of the pericardium, which has hitherto been so 

 narrow, a process which would have, as a natural result, the 

 pushing of both kidneys more towards the definitive left side 

 of the body than they were before. We have some evidence, 

 then, for believing that the changes which arc noticeable in 

 the position of the organs in the body in successive stages 

 are at first due to a rotation of the whole visceral hump upon 

 the head through an angle of 180°, but that after this is 

 complete a further apparent rotation affecting the posterior 

 region of the body only is induced by unequal growth and 



