Terrestrial Amphipoda — Hurley 
117 
living in South African indigenous forests 
contains only the small fibrous particles of 
plants and other woody detritus.” 
Grimmett (1926) attempted to correlate the 
distribution of male talitrids with the nature 
of the forests in which they occurred and was 
led to this statement. "The males of [Paror- 
chestia sylvicola] are known to be rather rare. 
All the specimens collected were therefore 
determined for sex, the large flattened front 
legs of the male being, on the suggestion of 
Dr. Chilton, used as a guide. It was found that 
in a total of 383 specimens from the beech- 
forest locality, 43 , or 11.2 per cent were males, 
while in a total of 333 from the tawa forest no 
males were discovered, though each specimen 
was carefully examined with a dissecting lens. 
Moreover, the males in the former were fairly 
evenly distributed throughout all the samples. 
It would thus appear that males are extremely 
rare, or are not produced in the lower-altitude 
forest during this portion of the year. Tem- 
perature, dependent on altitude, is suggested 
as the environmental factor most likely to be 
involved.” 
Unfortunately, there is a simpler explana- 
tion which makes his conclusions of little 
value. Almost certainly he was dealing with 
two species, one an Orchestia with a large well- 
developed second gnathopod in the male, 
and the other a species of Tal/trus with the 
feebly developed, femalelike second gnatho- 
pod in the male which is characteristic of that 
genus (cf. Fig. 3). It is worth noting that 
Forster (1954) finds no evidence of altitudinal 
speciation or correlation between distribution 
and type of forest cover in the opiliones, and 
I believe this finding applies equally well to 
the amphipods. 
However, males are often absent from 
samples— Grimmett ’s figures suggest a nor- 
mal proportion of one male in ten— but 
whether this is due to ecological factors is 
doubtful. When collecting by hand, there is 
possibly more chance of favouring one sex, 
due to such things as size and agility differ- 
ences between sexes, or the possibility of 
sexual preferences for different depths in the 
leafmould. The season of the year, the biology 
of the species concerned, and location of the 
sample may affect the percentage of males. 
There is also no evidence that Grimmett’s 
figures are the norm for all species. 
SPECIATION 
In spite of our relatively poor knowledge of 
the cryptozoic amphipods, the number of 
species already known is surprisingly high 
and past experience suggests that future work 
will reveal many more. From the New Zealand 
region alone, some 14 species are known, and 
the fauna is by no means intensively studied. 
There are two lines of development towards 
the terrestrial environment, represented by 
Talitrus and Orchestia (and perhaps a third by 
Talorchestia) . The supralittoral species of these 
genera form a basically compact group, vary- 
ing generically only in combinations of gna- 
thopod shape and other comparatively minor 
morphological variations — minor, that is, 
compared to generic distinctions -in other 
families. There is, in fact, a tendency for 
Talorchestia and Orchestia to intergrade. How- 
ever, the morphology of the terrestrial species 
of Orchestia and Talitrus suggests that they 
have arisen independently from supralittoral 
species. 
It is also of interest that, whereas littoral 
species tend to be somewhat cosmopolitan, as 
may be seen by comparing the faunal lists for 
New Zealand and South Africa, the terrestrial 
species are noticeably localised. 
It is not difficult to suggest reasons for the 
proliferation of species. The island nature of 
the Indo-Pacific provides textbook condi- 
tions for speciation due to reproductive isola- 
tion. The terrestrial fauna of the subantarctic 
islands, as recorded by Chilton (1909), sug- 
gests speciation through geographical isola- 
tion. With some exceptions, the terrestrial 
species of Polynesia and Melanesia also sug- 
gest geographical isolation. 
Within New Zealand, Forster (1954) and 
Dell (1955) have suggested a possible cor- 
