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 wroratus with the female ot 
Cancer borealis. 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 borealis, 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 egg 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 yenera 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 Zoéa form to the Brachyura, and 
the second to the Macrura. Bell, in the Introduction to 
his ‘ British Stalk-eyed Crustacea,’ reproaches Thompson 
tor coming to the conclusion ‘that Slabber lost his Zoéa, in 
