564. WILLIAM BATESON, 
no insistance is placed on the following suggestion, the plausi- 
bility of it is such that it cannot be omitted. On a previous 
occasion I have called attention to the fact that the pore which 
in Amphioxus leads into the left anterior body cavity is ob- 
viously homologous with the proboscis pore of Balanoglossus, 
which leads from the left horn of the anterior body cavity. In 
some species of Balanoglossus the opening of this pore is placed 
medianly, though opening into the left horn. Now, supposing 
the preoral lobe to atrophy, as in an Ascidian, so that the 
neural pore came to open into the buccal cavity, as occurs in 
these forms, it is clear that any pore placed dorsally between 
the neural pore and the mouth will then be directed ventrally, 
and open into the pharynx below the end of the nervous 
system. This is precisely the position occupied by the ciliated 
pit of an Ascidian, which leads into the gland described by 
Julin (‘ Arch. de Biol.,’ 59). Hence with this pore and gland 
of an Ascidian the proboscis pore and gland of Balanoglossus 
may be compared. Next, supposing the end of the nervous 
system to dilate and form a brain which bends. up by a cranial 
flexure it follows that on the atrophy of the proboscis (or rather 
before the proboscis was formed, this being peculiar to En- 
teropneusta) this pore will lie in the dorsal wall of the stomo- 
dum, i. e. in the position of the pituitary body. More than 
this, any gland attached, as is the proboscis gland, to the end 
of the notochord, will, when this is flexed by the cranial 
flexure, be bent backwards with it to the place where its end 
comes to lie, i.e. above the pituitary involution. In this way 
the double structure of the pituitary body becomes intelligible. 
Tf these views are correct the pituitary body and its pore is to 
be regarded as the rudiment of a primitive excretory organ, 
which originally opened dorsally. 
I have elsewhere shown the prima facie resemblance of the 
anterior body cavity with its pore in Amphioxus to that of 
Balanoglossus, which in the Tornaria development is formed 
from the water-vessel (Spengel). This water-vessel is precisely 
similar to that of Echinoderms, being otherwise without parallel 
among animals. 
