MUSEUM OF COMPARATIVE ZOOLOGY. 225 



able that they have all observed the same structure. Whether or not 

 any portion of the epiphysis as I have found it in Phrynosoma cor- 

 responds to the paraphysis of Selenka, or the ependyma of Hoffmann, 

 can of course be determined only by studying the development of this 

 portion of the brain, 



Bearing in mind the highly vascular condition of all part:; of the 

 parietal organ, the numerous large blood-vessels surrounding the vesicle 

 in P. Douglassii, and the great sinus in the same region in P. coronata, 

 the sinuses of the epiphysis in both species, as well as the great quan- 

 tity of blood contained in the much folded anterior wall of the epi- 

 physis, it seems to me impossible to escape the belief that, in this genus 

 at least, the organ must have some physiological significance. Leydig 

 ('89) has expressed the opinion that it belongs primarily to the lymph 

 system. From what has already been said, it is evident that I cannot 

 accept this conclusion ; but it does appear to me highly probable that 

 the structure has become secondarily of such a character. From the 

 numerous instances of change of function in the animal organism to 

 which attention has been directed by Dohrn ('75), Kleinenberg ('86), 

 Lankester ('80), Weismann ('86), and others, there are certainly no 

 a priori objections to such a view, and it seems to afford more nearly a 

 satisfactory explanation of the present condition of the organ than does 

 any other. 



Cambridge, August 15, 1890. 



vol. xx. — no. 8. 15 



