404 



THE DEVELOPMENT OF THE CHICK 



the condition found in many mammals, the cortical cords of the 

 birds corresponding to the cortical substance, and the medullary 

 cords to the medullary substance of mammals. The medullary 

 cords are often called phseochroms or chromaffin tissue on account 

 of the specific reaction of the constituent cells to chromic acid, 

 and their supposed genetic relation to tissue of similar composition 

 and reaction found in the carotid glands and other organs asso- 

 ciated with the sympathetic system. 



FIG. 231. Photograph of a cross-section of an embryo of 8 days through the 

 ostia tubse abdominalia. 



M Vt t S A^ k f abdo " linal air : sac - O. T. a., Ostium tub abdominale. 

 Rec nn ett '?f senter y- P 1 ' C ' r -> !> Right and left pleural cavities. 

 *na P cav H ' h g ht P neumat />-enteric recess. V. c. a. I., Left anterior 

 va. K,, rib. Other abbreviations as before. 



The embryonic history has been the subject of numerous 



investigations, and has proved a particularly difficult topic, if 



to judge from the variety of views propounded. Thus 



' instance it has been maintained at various times: (1) that 



