ITS DIFFERENT PHASES OF DEVELOPMENT IN THE ANIMAL SERIES. 105 
11. It was at one time supposed that the red colour of the “red blood-corpuscles” 
of the Vertebrata is dependent on the iron which they contain, but latterly chemists 
have come to the conclusion, that though iron is essential to the “ red corpuscles,” it 
is not so to their colouring matter. 
12. In reference to this question, it occurred to me that it would be interesting to 
ascertain whether the corpuscles of the blood of an invertebrate animal, notwith- 
standing their slight degree or total want of colour, contain iron. 
13. Accordingly I collected some of the corpuscles of the blood of the Crab, which 
it is easy to do in consequence of the mode in which they collect together after 
the blood is drawn, as described in Memoir II. of this series, and in consequence of 
the plasma not coagulating. These I dried carefully and sent to my friend Professor 
Graham, who was so kind as to undertake to test them for iron. 
14. The annexed letter, from Mr. Graham, will show that the blood-corpuscles of 
the Crab, though but slightly coloured, do contain iron. 
“Dear Jones, 
“ I should have communicated sooner the result of the examination of the white 
corpuscles of the blood of the Crab, of which you sent a small quantity in a dried 
state, amounting to two or three tenths of a grain. It is that they contain a sensible 
quantity of iron, perhaps as much as red corpuscles. 
“ Yours, dear Sir, 
“ Most truly, 
“ Thomas Graham.” 
“ University College, Nov. 29, 1844.” 
15. Of course the presence of iron in the corpuscles of the blood of the Crab is not 
alone a proof that the red colour of the “ red corpuscles” of the blood of the Verte- 
brata is not owing to iron ; it is merely a proof that iron in equal quantity may exist 
in corpuscles without imparting to them a decided red colour, such as is presented 
by the “ red corpuscles” of the blood of the Vertebrata*. 
Comparison of the Corpuscles of the Blood of the Invertehrata with the Corpuscles of 
the Lymph of the Vertebrata. 
16. In the very respect in which the blood of the Invertebrata differs from that of 
the oviparous Vertebrata generally, viz. the absence of nucleated cells in the decidedly 
coloured stage, it resembles their lymph'f- (Memoir I., pars. 101 to 105.). 
shown to be the true analogues of the “red blood-corpuscles” of the oviparous Vertebrata, viz. the nucleated 
cells, Mr. Newport considers to be an early stage of the corpuscles which I have described in the same blood 
under the name of granule-cells, the former, according to him, becoming the latter by the development and 
accumulation of granules in their interior. 
When thus filled with granules, the cells, he appears to believe, burst, and the granules, thus set free, become 
the alleged analogues of the “red corpuscles” of the Vertebrata. 
* The coloured plasma of the blood of the Crab gave unquestionable indications of iron. 
f This conclusion, it is to be particularly observed, is to be distinguished from a view first promulgated by 
p 2 
