73 



same cliauges in the blood. The A or loAveiing of the 

 freezing' point for some examples taken at Port Erin was 

 as folloAvs (Beckmann's Freezing Point apparatus used) : 



Sea Welter in which Pecten were living A — 1"910 

 Blood from P. maxinuis - - A — 1'910 



- - A — 1-905 



- - A — 1-920 



An oyster or cockle placed in fresh water mig-ht 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 cla^jpiug 

 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 slightly 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 leucoc3'tes are amoeboid 

 corpuscles which have iine bristle-like pseudopodia, often 

 brauched and by means of which they can move slowly 

 (hg. 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 cJiidiiis are formed (fig. 7, L. el.). The 



