290 THE ZOOLOGIST. 
thereby give a fresh store to the hemoglobin. They are, 
therefore, respiratory ducts, just like the gills of Balanoglossus, 
of Amphioxus, or the Salmon. ; 
Functionally, then, they are similar; but what about the 
structural resemblances? Gills, you will remind me, are made 
not only by inpushings from without, but by outpushings from 
within, which meet and fuse with the inpushings. Well, such a 
thing does obtain among the Nemertinea, too; the mass of cells 
into which the canals from without extend are derived primitively 
from the walls of the cesophagus. 
Let these make our third point, or rather, the third point of 
Prof. Hubrecht. When we come to sum them up shortly we may 
state our points thus :— 
(1). Nemertean worms have a hollow structure which in 
position, and possibly in developmental history, agrees with the 
notochord of the Chordata. 
(2). The proboscis of most Nemertines has the same relations 
as the hypophysis cerebri of some Chordata, and that of a few 
Nemertines the same as that of most Chordata. 
(3). Laterally placed respiratory grooves in some Nemer- 
tines come into relation with outgrowths from the wall of the 
cesophagus. ; 
Before accepting the justice of the conclusions to which we 
seem to be led, let us repeat the scientific version of Danton’s 
famous saying about the orator, “ De la doute, encore de la doute, 
et toujours de la doute.” 
Are there no difficulties remaining? You will see one ina 
moment, I hardly doubt. You will say that while Chordates have 
the nerve-cords placed dorsally, all worms have them placed 
ventrally ; and you would be almost correct, yet not quite. 
Among all the remarkable discoveries which have been made 
in the quarter of a century that has elapsed since Mr. Darwin 
published his ‘Origin of Species,’ none are of greater value or 
significance than those which affect our knowledge of the evolution 
of the nervous system of animals. 
The simplest forms, such as Ameba, have no nervous system 
at all, but the whole surface of their body shows itself able to 
respond to external stimuli; in the lowest group of the Metozoa, 
the Sponges, a nervous system is, also, said to be absent. But 
this is not correct; Prof. Charles Stewart has found that the 
