NURSING ECHINODERMS. 
63 
Mammalia is confined to the protection it affords to the young’, 
which are, as Professor Wyville Thomson says, merely retained 
in a kind of commensal connexion with the parents until they 
are in a condition to shift for themselves ; the young animals 
do not appear to be nourished directly from the parent. 
As to the reason for the prevalence of such a mode of repro- 
duction among the Echinodermata of the southern seas, often 
in species whose near allies in other seas show a totally different 
series of phenomena, it is exceedingly difficult to form even a 
probable conjecture. The arrangements are evidently protec- 
tive, but against what ? From the remarks made by Sir C. 
Wyville Thomson he would appear inclined to consider the phe- 
nomena to have their raison d'etre in climatal causes, and yet 
he says that he is not 44 in a position to affirm that in these 
high southern latitudes direct development is universal in the 
sub-kingdom,” and he adds, 44 1 believe, indeed, that it is not 
so ; for species of the genera Echinus , Strongylocentrotus , and 
Amblypneustes run far south, and a marsupial arrangement 
seems improbable in any of these.” Nevertheless, it is a re- 
markable fact that during the southern cruise of the Challenger 
between the Cape of (rood Hope and Australia only a single 
form of Echinoderm 44 pseudembryo ” was taken in the towing 
net, and that was supposed to be the larva of a Chirodota from 
the presence of calcareous wheel-like bodies in its skin. 
