40 MR. GULLIVER ON THE RED CORPUSCLES OF A SHARK. 



of its frequenting- brackish-water and of its growing in it 

 with luxuriance, but we also know of its occurrence not 

 only in water in which the trace of nrarine admixture has 

 been quite too small to justify the epithet of brackish, but 

 even in water which has been absolutely free from any such 

 admixture. I believe that this interesting and beautiful 

 hydroid has been introduced into tliis country on foreign 

 timber, and that it is now like the freshwater mollusc Dreis- 

 sena polyinorpha which seems to have had a similar introduc- 

 tion, gradually advancing inland by our canals and rivers. 



Size of the Red Corpuscles of the Blood of the Porbeagle 

 or Beaumaris Shark (JLamna cornuhicd). By George 

 Gulliver, F.R.S. 



Having been present at the landing of this fish at Hastings, 

 November 10th, 1871, I took the opportunity of procuring 

 some of its blood. The fish was a male, eight feet three 

 inches in length, and 305 pounds in weight, and was taken 

 in the herring nets a few miles off Rye. I lost no time in 

 sending to Professor Flower a notice of the capture, and he 

 has secured the entire animal, so that we are likely to have a 

 good account of it in the Museum of the Royal College of 

 Surgeons. The mean long diameter of the red blood-cor- 

 puscles of the Porbeagle measured Tri^rd of an inch, and the 

 short diameter x-sVot'^- More than half a century after 

 Hewson's discovery of their large size in the Skate, Professor 

 Rudolph Wagner was, I believe, the first to show the large- 

 ness of these corpuscles in the other Plagiostomes. My 

 measurements, long since published, are to the same effect ; 

 so that, as regards size, these corpuscles have, in contra- 

 distinction to those of Teleostei, a batrachian character, but 

 are not so large as the same corpuscles in Lepidosiren. And 

 now the measurements of the blood-disks of the great Shark 

 show them to be so nearly alike in magnitude to those of the 

 small dog-fish and other Selachii as to support my former 

 observations, that in one and the same family of fishes and 

 reptiles there is little, if any, relation between the size of the 

 blood-disks and the size of the species. And this is just the 

 reverse of the fact established by my old measurements, and 

 others since made (' Proc. Zool. Soc.,' Feb. 10th, 1870), of 

 the blood-disks of birds and mammals, showing that in many 



