A STUDY IN CARCINOLOGY. 59 
sand or other material from beneath the anterior part of tlie carapace, the 
raking action being facilitated by the five hirge spines on the lower margin 
of the propodus. Tlius a more or less clear water-way is kept on the under 
side of tlie anterior side of the thorax. 
When the iscbiomerus is drawn as far back as possible^ the carpus can be 
flexed inwards to form an acute angle with it, and the flattened propodus may 
then be folded back so far that its posterior margin fits into a groove in the 
merus and both it and the dactylus are pressed against the basal joints of 
the third maxillipeds. In this position also the propodus can be rotated 
outwards with a raking action so as to clear away sand from beneath the 
body, without any corresponding movement of the iscbiomerus and carpus. 
A close examination of the chelipeds leaves no doubt that tlieir main function 
is to keep open a passage for water down to their basal joints. From this 
point backwards water must pass in two streams to the posterior branchial 
orifices along passages roofed in^ [lartly by the overhanging edges of the 
branchioslegite, partly by the forwardly directed last pair of pereiopods. 
The inner walls of these passages are formed by theepimera of the eleventh, 
twelfth, and thirteenth segments, which are somewhat excavated and over- 
hung by the edge of the branchiostegites. Their outer walls are formed by 
the first three pairs of pereiopods, which are tucked up under the roof formed 
by the last pereiopods, the merus in each case being directed forwards, the 
carpus, propodus, and broad lanceolate dactylus downwards and backwards. 
Tlie segments of the pereiopods being broad and flattened and their margins 
furnished with fringes of stiff closely set hairs, they form a sort of basket- 
work or sieve the meshes of which are filled in by the fringes of hairs, and the 
whole apparatus is adapted to admit to the interior water from which sand 
and other solid particles have been strained. The strainer is made more 
effective by the dense hairy fringes on the edges of the branchiostegite, and 
the whole apparatus is completed and roofed in posteriorly by the flattened 
segments of the abdomen, which are likewise provided with dense fringes of 
stiff hairs. 
Whatever may be the position of the chelipeds, there is a ventral gap on 
either side between their basal joints and the first pair of the pereiopods. 
This gap is partly filled by the "epaulettes" projecting from the sterna of 
the eleventh segment ; the rest of the gap is bridged over by the stiff hairs 
projecting from all round the margins of the epaulettes and forming a very 
effective strainer. It is through these two gaps furnished with this efficient 
straining apparatus that the greater part of the respiratory current of water 
must find its way from the cavity raked out in the sand by the chelijieds 
underneath the anterior part of the thorax. 
The structure and arrangement of the pereiopods and their relations 
to the thoracic epimera and abdomen being as above described, it may be 
inferred that Ranina buries itself in the sand by the digging action of the 
