Humphrey, Brain of the Snapping Turtle. 99 



The pre-paraphysis is the homologue of the paraphysis of most 

 authors. Other authors that I have had access to consider the 

 paraphysis as an outgrowth of the prosencephal and this inter- 

 pretation has been accepted in the preparation of this paper, al- 

 though this view involves in the adult brain, some rather anom- 

 alous relationships as will be pointed out hereafter. 



The relation of these structures in Cliclydra is in most re- 

 spects similar to the generally accepted view. Immediately 

 cephalad of the origin of the epiphysis the supracommissure 

 arches across the diaccele connecting the habenae. The pial and 

 endymal layers of the epiphysis separate, the pia passing ectad 

 of the commissure and the endymal layer entad. Cephalad these 

 layers join again to form the thin membranous roof of the diaccele. 

 This membrane is in every way similar to and in fact directly 

 continuous with the plexuses of the diaccele, aula and paracceles. 

 It is composed of a single layer of flattened, cuboidal, endymal 

 cells with thin walls and lightly staining nuclei. Ectad of this 

 is the exceedingly thin layer of pia formed of flat cells that take 

 a yellowish red stain from the picric acid-fuchsin, enabling one 

 to follow the intricate foldings of the membrane. This mem- 

 brane grows dorsad of the brain tube almost completely sur- 

 rounding the epiphysis in a closely folded mass. In the adult 

 it is continued cephalad of the tip of the epiphysis and forms 

 the supraplexus. I believe this sac to be the homologue of the 

 Zirbelpolster of German authors and of the post-paraphysis of 

 Herrick. To call this "the second vesicle of the epiphysis," 

 as is done by some authors, is very misleading as it has abso- 

 lutely no connection with the epiphysis proper. The general 

 form of this structure as shown in sagittal sections (Fig. 30) is 

 that of an expanded, wide-mouthed sac opening into the dia- 

 ccele. Frontal sections (Figs. 27-29) also show this opening to 

 be quite wide. The cephalic wall of this sac, as shown in fig- 

 ures 27-29, consists of a single layer of this membrane stretch- 

 ing across between the solid walls of the diencephal, and slight- 

 ly folded in its course. Both sagittal and frontal sections of this 

 region show cephalad of this sac a second sac — the paraphysis. 

 Its general form is conical or pear-shaped with the base directed 



