162
R. K. DELL
even more efficiently to their environment than are animals in temperate or tropical waters.
It is not difficult to find differences between Arctic and Antarctic
conditions, it is only difficult to find differences of sufficient scope to
explain differences in the incidence of viviparity or brood protection.
Nor is the difference in incidence always marked. Hedgpeth (1969b) for
example, has noted that in some Arctic forms of the pycnogonid genus
Nymphon, the males actually carry the developing young about until
they are quite large. This habit has not been observed in any species
of Nymphon in the Antarctic. Hedgpeth believes that this may be
because the more abundant food available in the Antarctic makes such
a degree of parental care unnecessary. Such asimple explanation ignores
the many other cases of brooding and parental care amongst Antarctic
animals.
It seems to the writer that a basic fallacy in seeking explanations
of this Antarctic phenomenon stems from the method of proposing the
problem in the form, " why should this habit be developed by Antarctic
animals? ". A more fruitful line of enquiry might well result from
considering the problem from a different viewpoint such as, " why have
animals with a capacity for viviparous development been able to invade
Antarctic waters so successfully? '' or " why does the capacity for viviparous development give so many Antarctic animals an adaptational
advantage? ".
Changes of viewpoint in regard to the position of direct and indirect
development amongst the echinoderms has been outlined above.
Direct development may be more widespread than indirect. At least
it is an important method of reproduction. It may be significant that
the ophiuroids in which the habit is well developed outside the Antarctic
are one of the most successful groups in the Antarctic, and that the
best represented Antarctic groups amongst the echinoids are the
cidaroids and the spatangoids in which brooding, especially amongst
Southern Hemisphere members is reasonably common. The writer
(Dell, 1962) has shown that brood protection occurs much more commonly amongst chitons than had been thought previously. The Antarctic-Subantarctic occurrence in such forms as Hemiarthrum setulosum
is not therefore such an unusual occurrence.
It seem8 likely that no group that does not show some degree of
viviparity amongst its members elsewhere develops the habit in the
Antarctic. Even the 1 % of comatulids outside the Antarctic quoted by
Dearborn and Rommell (1969) as being viviparous is significant. Some
groups which generally have viviparity as the main method of reproduction have adapted themselves extremely well to the Antarctic. The
R. K. DELL
even more efficiently to their environment than are animals in temperate or tropical waters.
It is not difficult to find differences between Arctic and Antarctic
conditions, it is only difficult to find differences of sufficient scope to
explain differences in the incidence of viviparity or brood protection.
Nor is the difference in incidence always marked. Hedgpeth (1969b) for
example, has noted that in some Arctic forms of the pycnogonid genus
Nymphon, the males actually carry the developing young about until
they are quite large. This habit has not been observed in any species
of Nymphon in the Antarctic. Hedgpeth believes that this may be
because the more abundant food available in the Antarctic makes such
a degree of parental care unnecessary. Such asimple explanation ignores
the many other cases of brooding and parental care amongst Antarctic
animals.
It seems to the writer that a basic fallacy in seeking explanations
of this Antarctic phenomenon stems from the method of proposing the
problem in the form, " why should this habit be developed by Antarctic
animals? ". A more fruitful line of enquiry might well result from
considering the problem from a different viewpoint such as, " why have
animals with a capacity for viviparous development been able to invade
Antarctic waters so successfully? '' or " why does the capacity for viviparous development give so many Antarctic animals an adaptational
advantage? ".
Changes of viewpoint in regard to the position of direct and indirect
development amongst the echinoderms has been outlined above.
Direct development may be more widespread than indirect. At least
it is an important method of reproduction. It may be significant that
the ophiuroids in which the habit is well developed outside the Antarctic
are one of the most successful groups in the Antarctic, and that the
best represented Antarctic groups amongst the echinoids are the
cidaroids and the spatangoids in which brooding, especially amongst
Southern Hemisphere members is reasonably common. The writer
(Dell, 1962) has shown that brood protection occurs much more commonly amongst chitons than had been thought previously. The Antarctic-Subantarctic occurrence in such forms as Hemiarthrum setulosum
is not therefore such an unusual occurrence.
It seem8 likely that no group that does not show some degree of
viviparity amongst its members elsewhere develops the habit in the
Antarctic. Even the 1 % of comatulids outside the Antarctic quoted by
Dearborn and Rommell (1969) as being viviparous is significant. Some
groups which generally have viviparity as the main method of reproduction have adapted themselves extremely well to the Antarctic. The