FACT AND FICTION 59 



Say established the species Cancer irroratus in 1817, 

 but in 1859 Stimpson discovered that under one name 

 Say had combined two species, having been misled into 

 matching the male of Cancer irroratus with the female ot 

 Cancer horealis. The differences between the sexes which 

 often exist in Crustacea have more commonly led naturalists 

 into the opposite mistake of instituting a separate species 

 for each sex. Cancer horealis, Stimpson, occurs in the 

 same localities as Cancer irroratus, only being a heavier 

 and more massive species it does not equally court shelter 

 and retirement, but will rest entirely exposed on bare 

 rocks and ledges, or clinging to weeds amid the onset of 

 the waves. Yet the strength of its shell does not save it 

 from the gulls and crows which take advantage of its 

 venturesome position to carry it off for their own con- 

 sumption. 



It is not only the sexes of the adult crustaceans that 

 often differ considerably in appearance, but in many in- 

 stances between the Qgg and maturity there are stages to 

 be passed through in which the forms of the young are so 

 startlingly different from those of their parents that they 

 have been placed in different genera, until the relationship 

 was eventually proved or made probable. To these lar- 

 val stages various names have been given, some of them 

 borrowed from the names of the supposed genera to which 

 the young animals had been at first assigned. 



The Dutch naturalist, Martin Slabber, in 1769, was the 

 first to publish an account of a crustacean metamorphosis 

 so striking that, as he says, had he not himself witnessed it, 

 he should have placed the two forms in different genera. 

 Yet this singular observation was left barren, until in 

 1823 Mr. Vaughan Thompson was induced to follow it up, 

 with results that have since been far-reaching. One very 

 curious circumstance in this history is that the two forms 

 which Slabber figures evidently do belong to perfectly dis- 

 tinct groups, the first or Zoea form to the Brachyura, and 

 the second to the Macrura. Bell, in the Introduction to 

 his ' British Stalk-eyed Crustacea,' reproaches Thompson 

 for coming to the conclusion ' that Slabber lost his Zoca, in 



