350 JOHN WARREN 



paraphysis is more like that of Chrysemys but seems to reach its 

 highest development before the final stages and then to retro- 

 grade in size distinctly. 



In Chelone mydas, Humphrey (51), fig. 7, the paraphysis is long 

 and narrow as in Lacerta muralis while in Chelydra serpentina, 

 fig. 30, it is a large wide tube with some diverticuli and resembles 

 rather the paraphysis of serpents. Leydig (61) has described 

 the paraphysis in Tropidonotus natrix and Vivipara urcini, 

 Ssobolew (91) in Tropidonotus and Vipera berus, and Herrick (39) 

 has shown it in Eutaenia. In all these it is well developed and 

 resembles in general the paraphysis of Chrysemys and Lacerta. 



In birds the paraphysis was described in detail by Dexter (20). 

 It is greatly reduced in size and at its final stage is a very 

 small outgrowth with a narrow lumen and very thick walls. It 

 is much obscured by the diencephalic plexus, see his figs. 1-7 and 

 Kupffer's (57) 278, 288-289. 



But few observations have been made on the paraphysis in 

 mammals since Selenka's article on the opossum in '90. I have 

 observed it in a sheep embryo of 26 mm., fig. 38, as a short out- 

 growth rather narrower and more elongated than the paraphysis 

 of the oldest chick mentioned above. Francotte has shown it in 

 a twelve weeks human embryo and it has been modeled by Ewing 

 Taylor in a human embryo of 22.8 mm., H. E. C. No. 871. I have 

 also seen it in a human embryo, H. E. C. No. 1598, 28.8 nmi., 

 fig. 39. 



We see therefore that at the upper and lower end of the verte- 

 brate series the paraphysis is much reduced while in the middle 

 especially in the amphibia it is most highly developed. 



The paraphysis is a distinct organ of relatively insignificant 

 size in lower forms where it appears as a simple sack-like evagi- 

 nation, later giving off more or less side branches. In amphibia 

 its glandular character is most highly marked and this is true to a 

 lesser degree in reptilia. It is a mistake to say as some writers 

 have that in advanced stages the paraphysis becomes changed 

 into a sort of choroid plexus. This error is due to the fact that 

 the structure gives off many complicated tubules which are in 

 relation to a correspondingly complicated mass of vessels form- 



