18 
gradually incereases in size further backwards and becomes the foot 
proper, the lateral ones are at the same time considerably reduced. 
A transverse section of the f»ot has the form of a triangle, with 
the top turned downwards. Longitudinal sections moreover show 
that transverse folds are not altogether absent. Posteriorly where 
the ventral furrow is confluent with the anus the foot again loses 
its prominent position among the other longitudinal folds of the 
ventral groove. It gradually diminishes in size whereas its lateral 
neighbours increase, so that finally it again has the appearance 
given in fig. 34. 
Internally the foot is supported by connective tissue, and muscu- 
lar fibres, transverse as well as vertical (fig. 24), enter largely 
into its constitution. I find it very generally thickly filled with 
blood-corpuscles which may either serve towards distension and 
extrusion of the foot or which may here undergo & respiratory 
process, being separated from the surrounding seawater merely by 
the epithelium of the foot. This will be discussed more fully in 
connection with the circulatory apparatus. At the very edges of 
the ventral groove, where the ciliated epithelium is suddenly ex- 
changed for the spiniferous integument there appear to be another 
set of lacunae on each side: here at least a similar accumulation 
of blood-corpuseles directly under the epithelium may be noticed 
in most of my sections (ll, fig. 24). 
THE NERVOUS SYSTEM. 
The nervous system of Proneomenia is celosely analogous to that 
of Neomenia and perfectly fits into the type which has been estab- 
lished for the Amphineura and which is also found in the other 
representatives Chiton and Chaetoderma. 
However a few points of primary importance appear not to have 
as yet been noticed for the other genera of this class which give to 
the nervous system of Proneomenia a special interest in the dis- 
cussion about the affinities by which the archaie Mollusks (of 
which the Amphineura are certainly the nearest representatives) 
are related to other invertebrates. 
