122 
PACIFIC SCIENCE, VoL XIII, April, 1959 
water G.pulex, 12-18; and a littoral species of 
Gammarus, 8-12, Lawrence (1953) gives a 
figure of 6-14 eggs for the terrestrial Talitrus 
{T alitroides) eastwoodae, "the average thus be- 
ing almost identical with that of the littoral 
species quoted by Sexton.” Lawrence further 
states that, as far as is known, there is only 
one annual brood in T. eastwoodae, whereas 
G. chevreuxi breeds all the year round. Sexton 
(1928) writes of one female G. chevreuxi 
which was known to have 29 broods in a 
lifetime — 12 to 18 months is noted as the 
average breeding lifetime of a female G, 
chevreuxi-— 2Xidi Hynes (1955) says that G. 
pulex will breed five times in a year. 
So, as in other groups of invertebrates 
which have adapted themselves to terrestrial 
or fresh-water life, the eggs tend to be larger 
and fewer, an example of the general tendency 
for the more advanced species of a group to 
be more sparing in the production of the 
young. It is reasonable to expect that, as in 
other advanced groups, the eggs and young 
will have a longer developmental period, but 
when launched from the protection of the 
parental brood pouch the young will be more 
mature than those of the marine species. It is 
significant that Talitrus saltator takes con- 
siderably longer to mature than the 2 to IVi 
months required by the somewhat more hy- 
drophilous Orchestia gammarella (Verwey, 
1929, quoted by Williamson, 1951). 
Thus, changes in sexual habits and breeding 
of the supralittoral species are directly ad- 
vantageous in entering the terrestrial environ- 
ment. The suggested trend in delaying of 
egg laying until after moulting is most sig- 
nificant, and one would expect the truly ter- 
restrial species of Talitrus to have developed 
this trend even further, being limited ulti- 
mately only by the viability of the sperm. 
MOISTURE REQUIREMENTS 
Moisture requirements appear to have been 
met by the relatively stable nature of the en- 
vironment. The nature of the leafmould zone 
itself does away with much of the necessity 
for special adaptations, I have found that 
terrestrial amphipods in cultures uncontrolled 
for humidity vary specifically in resistance to 
changes of moisture, as would be expected 
from similar work on isopods (Edney, 1951) 
but that all species are extremely susceptible 
to dessication. Apart from these variations in 
resistance, no specific adaptations to mois- 
ture requirements have been observed. Ed- 
ney’s work on isopods (1951, 1954) suggests 
that adaptations to this environmental factor 
are to be found in behavioural and physio- 
logical rather than morphological factors. He 
believes that terrestrial isopods have not de- 
veloped the waxes characteristic of insect 
cuticles "which have contributed largely to 
their success as terrestrial animals.” 
However, there is evidence that such water- 
conserving adaptations as impermeable cuti- 
cles are not the only way of meeting the 
hazards of at least a limited degree of terres- 
trial life. "The ability to evaporate water 
rapidly, and thus to cool the body, may be of 
survival value when woodlice are exposed to 
high temperatures for short periods, particu- 
larly in littoral forms which may well have 
been intermediate in the evolution of terri- 
colous from maricolous isopods” (Edney, 
195 1^?). This is supported by various meas- 
urements of transpiration rates in cryptozoic 
invertebrates quoted in Edney (1954), sug- 
gesting that "high transpiration rates are gen- 
erally associated with cryptozoic arthropods.” 
Casual observations support the likelihood 
that the permeability of the exoskeleton of 
terrestrial amphipods is much greater even 
than that in isopods, and by inference, that 
transpiration rates may also be higher. Ter- 
restrial amphipods, when placed in 70-95 
per cent alcohol, immediately react vigor- 
ously, but in little more than 10 seconds show 
no further signs of life. Isopods, under the 
same conditions, have been observed to react 
for as long as 10 minutes before final quies- 
cence. I have also noted a similar differential 
rate in susceptibility to dessication. Lawrence 
(1953) likewise notes that Talitrus eastwoodae 
