4 
W. E. E. WELDON. 
in the protoplasmic tunic at its anterior end of the body (figs. 
1, 3, 10, Br.). It is composed of a mass of fibres, below which 
is a layer of nerve-cells. From some of these cells processes 
go downwards to the cuticle, which some, and probably all, 
perforate. At each side of the brain is a special group of 
these processes, which stain more deeply than those nearer 
the middle line, though they seem not to differ from the latter 
in any other respect. I unfortunately neglected to make 
macerated preparations of the fresh Haplodiscus while I 
was in the Bahamas, and I cannot therefore say more about 
these processes. There can, however, be little doubt that they 
are in some way sensory. 
A nerve having precisely the structure of the brain goes on 
each side for a short distance round the edge of the creature. 
The alimentary tract occupies the centre of the body, 
communicating with the exterior by a mouth (figs. 2, 10, M.), 
which is simply a small perforation of the ventral cuticle, 
round which the muscles and other tissues do not seem to have 
undergone any special modification. The alimentary tract 
itself consists of a large mass of protoplasm, continuous at 
the sides of the mouth with the general tunic of the body, and 
sending processes from every point to join the protoplasmic 
reticulum. Nuclei seem to be absent, except occasionally at 
the edges of the mass. Vacuoles are frequently found, con- 
taining generally small crustaceans in various stages of disin- 
tegration. In one series of sections the alimentary proto- 
plasm protruded from the mouth as represented in fig. 10, and 
it seems probable that during life it is capable of forming 
pseudopodia for the capture of prey. 
The reproductive glands consist of a single testis, 
which lies on the dorsal side of the body, vertically over the 
mouth, and a pair of ovaries, one on each side of the alimen- 
tary mass. 
The testis (figs. 2 and 10, Te.) is a mass of large, deeply- 
staining cells, lying in a meshwork of processes of the general 
reticulum, but not separated by any definite investing mem- 
brane from surrounding structures. The cells which form 
