60 A HISTORY OF RECENT CRUSTACEA 
changing the sea-water, and that the new form came from 
the added portion.’ The second form has been shown to 
correspond very exactly with the larval stage of a prawn, 
and from this Bell weakly argues that the observation of 
Slabber was correct, although the first form, as Bell had 
reason to know, was the larval stage of a crab, and in this 
Slabber correctly observed the gradual dwindling of the 
horns of the carapace. The minuteness and transparency 
of these infants and the readiness with which they perish 
will account for the confusion in regard to the principal 
change into which he appears undoubtedly to have fallen, 
but it is remarkable that such an error should have been 
in close agreement with the real facts of the case, that a 
discovery apparently so full of interest should have been 
neglected for half a century, and that then, when at length 
it was placed upon a solid foundation, the facts should 
have been hotly and stoutly disputed for a long series of 
years. In 1837 Milne-Edwards was still undecided on 
many of the details of the question, but as to the state- 
ment made by Vaughan Thompson in 1835 that the great 
French naturalist had been deputed by the Academy of 
Science to investigate the development of the Crustacea, 
that he had passed a summer in the Isle of Ré for that 
purpose, and had come to the conclusion that the Crustacea 
are born in their permanent forms, in all that, Milne- 
Edwards retorts, there is not a word of truth. He had 
never been in the Isle of Ré, he had never denied that 
some Crustacea underwent considerable changes, and he 
could only hope that Thompson was more careful in his 
observations than in his quotations. Notwithstandmg 
this sharp denial, Bell in 1853 still sends Milne-Edwards 
to the Isle of Ré, and wonders that observations which he 
never made should have led him to conclusions which he 
did not entertain. 
The larval stages of the American Cancer wrroratus 
have been studied by Professor S. I. Smith. As might 
have been expected, they agree very nearly with those 
of the European Cancer pagurus. In its latest stage 
the Zoéa still has a frontal and a dorsal spine that are 
