STRUCTURE AND DEVELORMENT OE REISSNER’s FIBRE. 13 
(fig. 9).” Tliis ‘^cone-like projection’^ is obviously tlie 
posterior end of tlie sub-comiuissural organ (cf. text-fig. 
2 , A, b), and this constitutes his only reference in this paper 
to this organ. 
Sargent apparently still continues in tliis paper to confuse 
the aquednctus Sylvii with the third ventricle, for he says 
(p. 448): ‘'In the adult Petromyzon Peissner’s fibre passes 
through the canalis centralis and the fourth ventricle, from 
which it enters the brain-tissue of the basal portion of the 
cerebrum, and passing through this emerges into the third 
ventricle. Here it breaks up into several trunks and con- 
tinues forward to the anterior portion of the ventricle, where, 
after further division, it enters the tectum.” The “basal 
portion of the cerebrum,” too, is somewhat vague, but Sargent 
means apparently the postero-ventral part of the optic lobes, 
and perhaps also of the cerebellum. 
Sargent further describes (’01) in the sinus terminalis 
of Amia, Raja erinacea and Petromyzon marinus, free 
“posterior canal cells,” which, he states,send forward “axons” 
to meet the backwardly growing Reissner’s fibre, and says 
(p. 447) : The fibre, then, is a nerve-tract composed of axons 
running in opposite directions, both cephalad and caudad. 
'ITie development of this apparatus as outlined for 
Amia is typical for all vertebrates” (my spaced t 3 qje). 
It is in this paper that Sargent, upon what appears to me 
to be altogether unsatisfactoi'y and insufficient evidence, first 
puts forward the optic refle.x theory, which he formulates as 
follows (p. 450) : “The apparatus which is the subject of this 
paper forms, I believe, a short circuit between the visual 
organs and the musculature, and has for its function the 
transmission of motor reflexes arising from optical stimuli.” 
Ilis text-fig. A (p. 449) offers a diagrammatic repre- 
sentation of the structure of this “ optic reflex apparatus,” 
but he wholly omits, so far as I can find, to make clear in 
what way he supposes the alleged axons of the “ posterior 
canal-cells” to be related to the cells of the “ Dachkern ” or 
other brain centre. 
