51 
NURSING ECHINODERMS. 
A S most of our readers are probably aware, the mode of 
development general among the Echinodermata is not 
direct, but complicated by the intervention of what has been 
called a “ pseudembryonic stage ” — a minute organism swim- 
ming by the aid of cilia, quite distinct in appearance from its 
parents, and producing the adult form by a process analogous 
to gemmation. The more striking forms of pseudembryos, 
when originally discovered, were regarded generally as inde- 
pendent organisms, and their peculiarities of structure led to 
their being taken as the types of several genera of ani- 
malcules, to which the names of Pluteus , Bijpinnaria , Auri- 
cularia , &c., were given. In some cases, indeed, the young 
animals could hardly be said to be true pseudembryos in the 
proper sense of the term, as their structure was merely compli- 
cated by certain provisional organs which were cast off when 
the perfect form was attained ; and in some cases the develop- 
ment was found to be absolutely direct, even in species nearly 
allied to others which had well-marked pseudembryos, just as 
we find among the Crustacea that the mode of development of 
nearly related species sometimes differs in the earlier stages. 
During the voyage of the Challenger , just completed, great 
numbers of interesting Echinodermata were procured, and 
among those obtained in the Southern Ocean there were many 
which not only presented an exception to the ordinary mode of 
development in their nearest allies, in the fact of the young 
animals being produced directly, and apparently without the 
intervention of a pseudembryo, or the formation of any pro- 
visional organs, but also exhibited certain curious arrangements 
of various parts, adapting these to furnish protection to the 
young during their helpless early stages. In some instances, 
indeed, the analogy of the arrangements with those prevailing 
in the pouched mammals of Australia is so strong as to justify 
the application of the term 66 marsupial ” to these Echinoderms. 
Sir C. Wyville Thomson has just described in the 66 Proceedings 
of the Linnean Society ” eight examples of these protective 
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