SEA-FISHERIES LABORATORY. AOS 
same changes in the blood. The A or lowering of the 
freezing point for some examples taken at Port Erin was 
as follows (Beckmann’s Freezing Point apparatus used) : 
Sea water in which Pecten were living A — 1:910 
Blood from P. maximus e : A —= 1°910 
- Fy by : - A — 1°905 
‘ ' i a ec Nee 99() 
An oyster or cockle placed in fresh water might live 
for some time without any change taking place in the 
osmotic concentration of the blood. This, however, is 
simply due to the animal closing the shell valves and 
completely shutting out the external medium from any 
contact with the body. In Pecten, on the contrary, as 
already pointed out, the two shell valves do not close 
perfectly, and, moreover, the animal persists in clapping 
the valves, so that a change in the outer fluid is followed 
by a change in the blood and immersion in fresh water 
proves fatal. ‘The electrical conductivity is shghtly less 
than that of sea water. If the blood is allowed to stand, 
after being drawn, the mass does not become jelly-like 
by coagulation as does crustacean blood, but a white 
precipitate forms, often in one large mass. The process 
can be watched under the microscope, and the precipitate 
will be seen to consist wholly of leucocytes which have 
collected together and left the fluid portion of the blood 
practically free from them. ‘The leucocytes are amoeboid 
corpuscles which have fine bristle-like pseudopodia, often 
branched and by means of which they can move slowly 
(fig. 7, L.). Sometimes these narrow bristle-like pseudo- 
podia prove to be the edge-view of: flattened lamellae. 
When the blood is exposed to the air, the corpuscles 
collect together, becoming entangled by the pseudopodia, 
and in this way clumps are formed (fig. 7, ZL. cl.).. The 
