1888 .] 
Mr D. M'Alpine on Bivalve Molluscs. 
199 
of egg-like bodies, large and small, yellow and colourless, and 
sometimes with the contents wholly or partially removed. In- 
numerable minute rounded bodies moving slowly about, and 
giving motion to neighbouring masses, only definitely seen under 
a high power of the microscope. In some specimens numerous 
Spirillum-like bodies were also observed. In addition to these there 
was a miscellaneous collection of various things — stray pieces of 
filamentous algse, small pieces of limbs of minute crustaceans, 
empty egg-shells, and inorganic matter. 
The most noticeable bodies present were Diatoms, yellow egg-like 
bodies, and ova of various kinds and sizes or spores. After deter- 
Qiining generally the nature of the food, I examined specially a male 
and a female,— the sexes being separate in Mytilus. The object 
was to see if either of the sexual elements occurred in the food. 
After examining spermatozoa from the deep salmon-coloured mantle 
of the male, I took some of its food from the stomach, and found 
spermatozoa there in great abundance. After viewing ova from 
the pale salmon-coloured mantle of the female, I likewise examined 
its food, and found occasional ova of its own present there. The 
presence of the animal’s own sexual elements in the food goes to 
show that what enters the mouth is not so carefully tested and tried 
as some would make us believe. 
A little consideration will show that there are grave difficulties 
in the way of getting food into the mouth by the direct interven- 
tion of the palps, although apparently so natural. 
Firstly, the direction of their currents is against it. 
Secondly, the particles conveyed by the gills are bound together 
by viscid material, and this arrangement is, against selection by the 
palps, rather in favour of rejection. 
Thirdly, the viscid secretion of the palps themselves likewise 
binds together particles for convenience of rejection. This viscid 
matter is also elastic. I have seen particles smeared with this 
viscid material carried the whole length of the body, along the 
muscular margin of the mantle, without breaking the thread, so 
that where it should have left the body it was pulled back again. 
This elasticity will enable the aggregated matter collected at the 
anterior end of the gills to form more readily into halls. Such balls 
of refuse matter are often met with, and sometimes they are shot 
