60 A HISTORY OF EECENT CEUSTACEA. 



cTianging 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 thab 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 Crastacea, 

 that he had passed a summer in the Isle of Ke for that ' 

 purpose, and had come to the conclusion that the Crastacea 

 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 Re, he had never denied that 

 some Crustacea underwent con.siderable changes, and he 

 could only hope that Thompson was more careful in his 

 observations than in his quotations. Notwithstanding 

 this sharp denial, Bell in 1853 still sends Milne-Edwards 

 to the Isle of Re, 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 irroratus 

 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 Zoea still has a frontal and a dorsal spine that are 



