£; PROBOSCIS PORES ” IN CRANIATE VERTEBRATES. 539 
“Proboscis pores” in Craniate Vertebrates, a 
Suggestion concerning the Premandibular 
Somites and Hypophysis. 
By 
Edwin S. Goodrich, F.R.S., 
Fellow of Merton College, Oxford. 
With Plate 28, and 3 Text-fignres. 
There is in Ampliioxus on the roof of the buccal cavity a 
deep pit known as Hatschek's pit, from its discoverer. Its 
blind, inner end extends upwards to the right of the noto- 
chord, while the lining epithelium is continuous at the opening 
of the pit with the areas of thickened ciliated epithelium 
which spread over the roof and sides of the buccal cavity. 
This ciliated organ is the wheel-organ of Johannes Muller, 
and was shown by him to drive a current of water and food- 
particles into the mouth. Van Wijhe ( 14 ) has since given a 
detailed account of its structure. An unpaired dorsal region 
extends backwards so as to surround the opening of the pit, 
then divides into right and left tracts. The two branches run 
towards the velum and then down the sides of the buccal 
cavity, but do not meet ventrally. As shown in Text-fig. 1, 
finger-shaped tracts extend forwards on the inner surface of 
the oral hood. These structures become more complicated in 
older specimens. The deeply staining epithelium of which 
Muller's organ is composed is formed of very closely packed, 
narrow columnar cells, whose nuclei form several layers, and 
whose outer ends bear each one cilium. Good figures of 
these cells have been given by Langerlians ( 8 ). 
