DEPARTMENT OF EMBRYOLOGY. 87 



experimental displacement; whether it slips back into its normal 

 position immediately after the operation or later, after the wound is 

 healed. His observations indicate the latter to be the case. There 

 was no evidence of rotation during the first 3 hours, at the end of 

 which time the wound had entirely healed. Specimens examined 

 between 16 and 34 hours after operation, when the labyrinth is still 

 a simple oval sac without canals, showed that rotation had occurred. 

 Dr. Ogawa also demonstrated that an ear-vesicle may be transplanted 

 from one species to another {Amhlystovia to Rana or vice versa) and 

 that, when placed in an inverted position, it rotates into the normal 

 posture by the end of the second week. The environmental influence 

 in the determination of posture is therefore effective even for the ear- 

 vesicles of species of a different order. 



In my own experiments, and in earlier ones of Dr. Ogawa, the 

 inversion of the vesicle at the time of operation was obtained by 

 rotation about the vertical axis, with the result that the lateral con- 

 cave surface was placed toward the brain. In his recent observations 

 Dr. Ogawa found that when the vesicle was rotated about the trans- 

 verse axis, recovery of position failed to take place in nearly half of 

 the cases, although the technique was otherwise the same as previously 

 employed. He does not regard this decreased tendency to rotation as 

 due to the difference in inversion axis, but more probably to the fact 

 that where the rotation is about the transverse axis the open side of 

 the vesicle is left in contact with the heahng wound, with which it may 

 become sufficiently adherent to interfere with rotation. 



DIGESTIVE TRACT AXD VASCULAR SYSTEM. 



The interest' ng development of the gastro-intestinal tract of the 

 opossum has been studied by Dr. C. H. Heuser. In this non-placental 

 animal the intrauterine period lasts only 13 days; 5 days after the 

 beginning of segmentation the immature animal is expelled from the 

 uterus and, by its own efforts, secures attachment to a teat in the 

 maternal pouch, where its development is completed. Nutrition is 

 made possible by the precocious growth and differentiation of the 

 gastro-intestinal tract, particularly the upper part of the small intes- 

 tine. By means of models and the study of sections. Dr. Heuser has 

 been able to trace the phenomenal alterations which this system 

 undergoes in the few days preceding birth and the first few days in 

 the pouch, whereby the rudimentary foregut, hindgut, and midgut 

 become converted into a series of structures capable of assimilating 

 milk. Only those portions of the body that play an accessory role, 

 such as the sucking mechanism and the forward extremities, take 

 part in this precocious growth. 



In our report of last year reference was made to the observations 

 of Dr. R. S. Cunningham on the striking morphological changes and 



