318 THE ORIGIN OF VERTEBRATES 
we see that Dohrn’s original view of the comparison of the vertebrate 
and the annelid led him to the conception that the vertebrate mouth 
was formed by the coalescence of a pair of gill-slits, and that the 
original mouth was situated somewhere on the dorsal surface and 
opened into the gut by way of the infundibulum and the tube of the 
hypophysis. This, also, was Cunningham’s view as far as the tube 
of the hypophysis was concerned. Beard, in 1888, holding the view 
that the vertebrates were derived from annelids which had lost their 
supra-cesophageal ganglia, and that, therefore, there was no question 
of an cesophageal tube piercing the central nervous system of the 
vertebrate, explained the close connection of the infundibulum with 
the hypophysis by the comparison of the tube of the hypophysis with 
Fic. 125.—DiagRamM TO sHOW THE MEETING OF THE FouR TUBES IN SUCH A 
VERTEBRATE AS THE LAMPREY. 
Ne., neural canal with its infundibular termination; Neh., notochord; Al., alimentary 
canal with its anterior diverticulum; Hy., hypophysial or nasal tube; Or., oral 
chamber closed by septum. 
‘the annelidan mouth, so that the infundibular or so-called nervous 
portion was a special nervous innervation for the original throat, 
just as Kleinenberg had shown to be the case in many annelids. 
Beard therefore called this opening of the hypophysial tube the old 
mouth, or paleostoma, Recently, in 1893, Kupffer has also put 
forward the view that the hypophysial opening is the paleostoma, 
basing this view largely upon his observations on Ammoccetes and 
Acipenser. 
As is seen in Fig. 125, the position of. this paleeostoma is a very 
suggestive one. At this single point in Ammoceetes, four separate 
tubes terminate; here is the end of the notochordal tube, the termina- 
tion of the infundibulum, the blind end of the nasal tube or tube 
