48 
Proceedings of the Royal Society of Edinburgh. [Sess. 
VII. — Experiments on the Respiratory Mechanism of the Shore 
Grab (Oarcimis msenas). By Robert K. S. Lim. (From the 
Laboratory of Physiology, Edinburgh University.) Communicated 
by Sir E. A. Schafer. 
(MS. received November 3, 1917. Read December 3, 1917.) 
While carrying out some immersion experiments on Carcinus mamas, 
I had occasion to investigate its respiratory mechanism. Comparing my 
results with those recorded in the literature of the subject, I found that I 
could add a few new observations. 
Technique. 
The materials used consisted of a large glass basin, containing 2| inches 
of fine sand and enough sea- water (Millport) to cover the sand to a depth 
of about an inch, this being found sufficient to completely immerse the 
crabs. By means of a small syringe a fine suspension of Indian ink in 
sea-water was then injected into the fluid surrounding the animals, whereby 
the presence and direction of the respiratory currents could be detected. 
Lastly, it may be of importance to note that the habitat of the crabs 
used was a rocky patch in the middle of a large beach of fine sand. 
Experiments with Crabs lying on their Backs on the Surface 
of the Sand but wholly Immersed in Sea- Water. 
Exp. I. — When Indian ink was injected near the prostomial chamber 
it was swept outwards by a strong exhalent current proceeding from the 
whole breadth of the chamber. The direction of the current was forward 
and generally parallel to the median line of the crab, although sometimes 
it deviated to one or other side. 
Occasionally an inlialent current was noticed between the anterior 
borders of the third maxillipedes and the adjacent carapace. This current 
was very brief, the ink soon emerging from the sub-branchial clefts, i.e. the 
spaces between the base of the thorax and the branchiostegite of each side. 
Frequently no currents could be observed at all. 
Exp. II. — When injected close to either sub-brancial cleft the ink was 
sucked in or inhaled throughout the whole opening, more especially round 
the coxa of the chela, and later it could be seen emerging from the 
