156 JOURNAL OF SCIENCE. 
punctatus, and I have added Philougria rosea. Of these all 
appear to be peculiar to New Zealand, except Porcellio graniger, 
which is also found in Tasmania and at Melbourne (Haswell’s 
“Catalogue of Australian Crustacea,” p. 280), and Phzlongria 
rosea, which is found in England. The latter isa most remark- 
able case; so far as I can tell from the figure and description 
given by Spence Bate and Westwood, the New Zealand speci- 
mens do not differ in any character of specific importance from 
those found in England. Hence at first I thought it must have 
been introduced ; but this can scarcely be the case, for I have 
taken it in abundance at Christchurch and Eyret)n, in the bush 
at East Oxford and at View Hill, and in South Canterbury at 
Rangitira and Kakahu, near Temuka. An animal of such feeble 
powers of locomotion could scarcely have spread so far in sucha 
short time. 
In considering the close resemblance between the terrestrial 
crustacea of widely separated countries, the question forces itself 
upon us—Have all terrestrial species arisen from one marine an- 
cestor, or have those of one country arisen quite independently 
of those of other countries—the resemblances being the result of 
similar conditions ? Suppose the marine ancestor of the terres- 
trial Isopoda to be widely spread and to inhabit the shores of, 
say, New Zealand and England, and that in each case certain 
animals began gradually to leave the sea and make their home 
on the land, at first keeping within reach of the spray, as Lzgza 
still does, but afterwards leaving the sea altogether, would not 
the new conditions in which these animals would be placed, being 
practically the same in both countries, produce in each case the 
same effect, so that the variations which would be preserved 
would be the same in the two cases, and hence the animals, al- 
though arising independently from the same marine ancestor, 
might so far resemble one another as to be placed in the same 
genus, or even in the same species? We know that this is true 
to a certain extent at any rate, for the terrestrial Amphipoda and 
Isopoda have without doubt arisen independently, and yet in both 
the inner antenne have become very small—rudimentary in the 
Isopoda, nearly so in Amphipoda,—and in both the mandible 
has lost its palp. If this principle admits of wider application, 
we may perhaps be able to understand the resemblance between 
the terrestrial crustacea of widely separated countries without 
having to fall back upon means of dispersal at present unknown. 
I am quite aware that the explanation I have advanced is not 
new. It is pretty muchthe sameas the “convergence of charac- 
ter” insisted upon by Mr. H.C. Watson (see “Origin of Species,” 
p. 100) ; but while he contends that the descendants of two dis- 
tinct genera may converge into one, I think the case of the ter- 
restrial crustacea shows that the descendants of the same genus 
may in two countries independently give rise to the same new 
genus. 
The Isopoda appear to have got a start of the Amphipoda, 
and to have taken to a terrestrial life much sooner, for they 
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