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PACIFIC SCIENCE, VoL XIII, April, 1959 
some supralittoral or "semiterrestrial” amphi- 
pods, and found that in Talitrus saltator the 
female is held by the male with the aid of the 
stout antennae and the peraeopods, whereas 
"holding” in marine and supralittoral species 
is normally done with the aid of a greatly 
developed second gnathopod. Talitr us saltator 
is, however, the only species of Talitrus which 
shows this marked development of strong 
antennae. The other, more truly terrestrial, 
species of Orchestia and Talitrus have slender 
antennae. Since most of them also lack the 
large male "grasping hand” of the supralit- 
toral species, it is likely that some further 
change in sexual habits has taken place. (A 
few terrestrial species retain the large "grasp- 
ing hand.”) 
In the Gammaridae, the eggs are laid al- 
most immediately after copulation, the time 
of laying in some species being determined 
by the time of copulation, in others by the 
time of moulting. In T. saltator, and probably 
in other talitrids, the time of laying is de- 
termined by the time of moulting. Laying 
takes place 4 days after moulting, but copu- 
lation may take place any time from 1 to 4 
days before laying. 
Williamson suggests that the eggs of the 
supralittoral Talitridae are fertilised in the 
brood pouch, and rules out both internal in- 
semination and internal fertilisation. The 
spermatozoa, which are already present when 
laying takes place, are then most probably 
activated either by a secretion of the unferti- 
lised egg or by a secretion which the female 
releases during laying. Spermatozoa of T. 
saltator can live at least 4 days in the brood 
pouch of the female, probably because of 
their inactivity and perhaps also because of 
their relatively large size (about 400 microns 
in length). 
More tangible developments correlated 
with the terrestrial environment are evident. 
In aquatic species of Talitridae, the male nor- 
mally carries the female around for some days 
before moulting, and copulation occurs im- 
mediately after moulting. "The carrying po- 
sition adopted by . . . Gammarus ... is 
obviously not suited to terrestrial conditions, 
. . . but it is probable that the aquatic ances- 
tors of the Talitridae employed this form of 
carrying, and it is still found in the more 
aquatic members of the family (Hyale spp.)” 
(Williamson, 1951). 
In the supralittoral species, there is no 
carrying before moulting. "Associated with 
the terrestrial habitat, therefore, we see not 
only modifications in the method of carrying, 
but also a great reduction in its duration” 
(Williamson, 1951). 
From these facts, Williamson concludes 
that the delayed egg laying, associated with 
the longevity of the sperm, has an adaptive 
significance. Where the moult governs the 
time of laying, the delay increases the chances 
of mating by increasing the time, between 
moulting and laying, in which mating can 
take place; furthermore, the male does not 
have to carry the female. On the other hand, 
mating in aquatic forms "can take place over 
a period of several days before the moult, and 
the probability of mating would be very little 
increased if egg laying were delayed for a few 
hours, or even days, after the moult” (Wil- 
liamson, 1951). 
Correlated with the terrestrial environment, 
there is also a reduction in the number of eggs 
produced. In most species of terrestrial am- 
phipods, I have found the number of eggs in 
the brood pouch ranges from 1 to 10, e.g., in 
Talitrus sylvaticus the average is between 3 and 
4. Yet in marine genera of the same family, 
the number carried by an ovigerous female of 
similar size may be many times this. An 
Allorchestes novizealandiae female taken at ran- 
dom carried l6l eggs, the greater carrying 
capacity of the animal being in part due to 
the much smaller size of the eggs. 
Sexton (1924) has shown a decrease in 
number of eggs produced by species of Gam- 
marus from marine to pelagic species. Gam- 
marus locusta, a marine species, has as many as 
143 eggs in a brood. The brackish -water G. 
chevreuxi has 30-40 per brood; the fresh- 
