THE PINEAL BODY 



39 



SgM^^^^ 



M 



Fig. 8 Schematization of the pineal region in Mammals, according to Stud- 

 nicka, 1905. 



Ds., dorsal sac; Ch., commissura habenularis; R., recessus pinealis; Ep., proxi- 

 mal portion of the pineal organ (epiphysis) ; Cp., commissura posterior; M., 

 midbrain. 



In the light of the phyletic review just given concerning the 

 structures constituting the pineal region, it becomes clear that 

 any satisfactory consideration of the epiphyseal complex must 

 take into account the characters of the parapineal organ as 

 well as those of the pineal organ. It seems advantageous to 

 discuss the comparative embryology of these two parts and 

 then to consider the phyletic characteristics of each of them 

 separately. In this way the modifications of each organ may be 

 followed consecutively from one order to the next. 



5. THE COMPARATIVE EMBRYOLOGY OF THE EPIPHYSEAL COMPLEX 

 1. The development of the epiphyseal complex in cydostomes 



According to Studnicka ('93) 384 and other observers, a small 

 evagination in the caudal portion of the roof-plate of the inter- 

 brain makes its appearance as a simple and single protrusion 

 from the roof. This is the pineal organ. There can be no 

 question but that it develops first of the two elements in the 

 epiphyseal complex in these forms. The anlage of the pineal 

 organ increases greatly in size so as to present an end-sac or 



