194 EDWARD MCCRADY, JR. 



Selenka (1887, p. 160) claimed that no organs of touch are 

 present, but perhaps this question has not been approached 

 with adequate techniques. It is hard to imagine that the com- 

 plicated crawling movements with their necessary component 

 the clasping of the mother 's hair by means of the claws and 

 toes of the forefeet can be accomplished without some sort 

 of exteroceptive apparatus in the skin. 



The cisterna chyli. In the opossum the cisterna chyli is 

 not developmentally a dilatation of the thoracic duct. It is 

 derived principally from a mesenteric lymph sac which de- 

 velops in stage 35 and which is homologous with the mesen- 

 teric lymph sac of rabbit, pig and cat embryos. This secon- 

 darily establishes communication with a peri-aortic lymphatic 

 plexus which leads into the caudal end of the thoracic duct. 

 The peri-aortic lymphatic plexus later enlarges and forms 

 the cranial portion of the cisterna, which is permanently 

 rather plexiform. 



In addition to the rather poorly developed connections of 

 the mesenteric sac with the peri-aortic plexus in stage 35 

 .there is a well-developed connection with the peri-oesophageal 

 lymphatics. This curious arrangement is later abandoned, 

 only the peri-aortic connections being preserved. Doctor 

 Zimmermann has suggested that the temporary connection 

 with the peri-oesophageal lymphatics is associated with the 

 precocious development and functioning of the digestive tract. 



Among other minor changes in the lymphatic system at 

 about the time of birth, the jugular lymph sacs attain their 

 maximal size, and the axillary portions establish communica- 

 tions with the deep lymphatics of the forelimb. The thoracic 

 duct enlarges markedly in caliber, and caudally it attains 

 communication with the mesenteric lymph sac as described 

 above. 



No lymph nodes have been developed in any part of the body 

 at birth. 



The auditory ossicles. In examining the earliest stages in 

 the development of the ossicles in the opossum I have been 

 unable to find any clear connection between the stapes and 



