AGASSIZ. NATURAL HISTORY OF THE UNITED STATES. 345 
Save in so far as they include these coral forms, the orders Dig- 
cophorce and Hy droid a? of Agassiz correspond, collectively, to the 
class Hydrozoa , as extended in 1856 by Huxley. So that this 
fourth volume of his 4 Contributions,’ like the £ Oceanic Hydrozoa ’ 
of our colleague, has some claim to be regarded as a manual of the 
class in question. The differences between these two works are, indeed, 
striking enough ; their points of agreement less obvious. Neverthe¬ 
less, both are abundantly stored with original observations, but con¬ 
tain also much general comment and discussion of first principles. 
Both, therefore, are indispensable, as books of reference, to the 
working student. Again, while Professor Huxley’s work embraces 
a detailed account of the Siphonophora , the remaining orders of 
Hydrozoa (if we except such reference as is made to them in his 
4 General Introduction ’) being passed over, we find these very orders 
most fully treated by Professor Agassiz, whose remarks on the 
Siphonophora are limited to a few pages.* So that the two mono¬ 
graphs, in matters of fact as well as in matters of opinion, serve to 
supplement and render each other complete. 
So much, then, for the volume as a whole. Next, of its separate divi¬ 
sions, foremost among which comes Part III. :—on the Discophorce. 
In his opening pages Professor Agassiz brings forward certain 
views on the limits of the order in question, acknowledging all the 
extensions which it has recently received, and proposing to enlarge 
its boundaries yet further. We deem it right to direct attention 
more fully to this subject, as a department of systematic zoology 
instructive and interesting in its details, of which we would here 
present as brief and complete a resume as possible. And to do so 
the more profitably we shall adopt the simply historical mode of 
statement, which will be for our present purpose, at once the most 
popular and the most intelligible. « 
Linneus, the founder of genera, formed the genus Medusa for 
the reception of all the oceanic ccelenterate animals with which he 
was acquainted. About the same time, Patrick Brownf proposed 
the name of Beroe for one of these forms, which Linneus first 
associated with Medusa , and afterwards with Volvox, while O. P. 
Muller, Modeer, and others regarded it as truly generic. Towards 
the close of the last and commencement of the present century, we 
find both j Beroe and Medusa enriched by the discovery of numerous 
additional species, soon in their turn to become genera, and even 
families, the names of which are brought together in the 
systematic works of contemporary writers, especially of Cuvier and 
* We might extend this comparison by remarking that Professor Huxley’s 
observations were made chiefly in the Southern, those of Professor Agassiz in th 6 
Northern Hemisphere; while the work of the one was published on the Eastern, 
that of the other on the Western shore of the Atlantic, 
f The Civil and Natural History of Jamaica, 1756. 
