54 Papers from the Department of Marine Biology. 
nation of ridges and fringes of setzee which occupy the posterior wall of 
the stomach between the cardio-pyloric valve and the cesophagus. 
These structures act as a filter to retain solid particles when water is 
expelled, but owing to the fact that these are all of small size no definite 
suboesophageal valve is present. 
The food organisms which are thus taken into the cardiac chamber 
are all probably small enough to pass straight through the pyloric filter 
and chamber into the mesenteron, where they are digested; hence their 
customary absence from the cardiac chamber. This organ, though 
far too large for the requirements, has not been reduced in size since 
Hapalocarcinus acquired its present habits. The pyloric filter is 
preserved for the separation of occasional particles of larger size, but 
these must be rare, since they were never observed in the stomach. 
Almost certainly the crab must have the power of rejection of unsuit- 
able pabulum. 
Porcellana, amongst the Decapoda Anomura, obtains its food by a 
kind of net-fishing rather similar to that I have supposed occurs in 
Hapalocarcinus. The appendages are provided with very thick borders 
of hair, but particularly the third maxillipeds, on which they attain a 
considerable length, greater than that in the gall crab. Gosse has 
described the way in which Porcellana platycheles uses the third maxil- 
lipeds by making alternate casting movements “exactly in the manner 
of the fringed hand of a barnacle, of which both the organ and the 
action strongly reminded me.” I examined the appendages and 
the contents of the stomach. In the former case little reduction is 
shown (the protopodites of both maxille are bilobed and the mandibles 
possess a palp), but the thickness and strength of the fringe of sete, 
developed even on the mandibular palp, show that all the appendages 
are used for sifting and not for mastication. The stomach is usually 
fairly full of food, generally in small unrecognizable fragments, occa- 
sionally larger pieces of alge. The proportion of planktonic organisms 
is not great and this is no doubt accounted for by the habitat of Por- 
cellana under stones in littoral situations where the water is more usu- 
ally muddy than clear, and organic débris abounds. So that while a 
similar method of obtaining the food is practised in both forms the 
nature of the food differs. In Hapalocarcinus it is much more minute 
and entirely in the form of living organisms. 
It occurred to me that other of the higher Crustacea which had 
adopted a sedentary existence might have developed a similar dietary 
and alimentary apparatus. Pinnotheres lives within the depths of 
the mantle cavity of a mollusc or the tube of a worm. Its tiny chele, 
like those of Hapalocarcinus, show that it is in no sense a predatory 
animal. It might be expected that it would live on minute plankton 
like its host. If the size of the animal is to be taken into consideration, 
some species of this genus are not very much larger than the gall- 
