6 Paraphysis and the Pineal Region in Necturus Maculatus 
seen, which is extending caudad at nearly a right angle to its previous 
line of growth. If the roof of the telencephalon be closely examined a 
slight bulging will be seen just cephalad to the opening of the paraphysis. 
These two outgrowths into the fore brain mark the beginning of the 
choroid plexuses, which, therefore, have in their origin a very intimate 
and definite relation to the opening of the paraphysis, one arising caudad 
and the other cephalad to it. The epiphysis at this stage has increased 
considerably in size, and the cavity in its stalk is now permanently oblit- 
erated. The body of the organ overlaps the stalk a little behind, and is 
beginning to grow well forward of it. The posterior commissure, P. C., 
appears here for the first time, a distinct interval in the roof of the brain 
lying between it and the stalk of the epiphysis. 
Fie. 9. Embryo of 17.5 mm. Harvard Embryological Collection, Sagittal 
Series, No. 540, Sections 113-115, & 63 diams. 
Fig. 9 is a section through the brain of an embryo of 17.5 mm. The 
paraphysis has increased in length, and from its distal end, which is 
somewhat enlarged, small tubules are given off. The whole tube is tipped 
somewhat forward. The choroid plexus is now well developed, and con- 
sists of two distinct parts, one dorsal and one ventral. ‘The dorsal part 
corresponds to the velum, which has grown caudad as far as the mid brain 
and has absorbed a large part of the post-velar arch. The ventral part is 
developed from the original paraphysal arch, and is growing towards the 
floor of the fore brain. Burckhardt (3) refers to these plexuses as 
“nlexus medius” and “ plexus inferioris,” respectively, and Mrs. Gage 
(13), who studied them in Diemyctylus, where the anatomical conditions 
closely resemble those of Necturus, names them the “ diaplexus” and 
“ »prosoplexus.” Prof. Minot has suggested the terms diencephalic 
