346 Prof. Allman on the Construction and 
polypoid portion to the vegetative mycelium of a mushroom, and 
the medusoid portion to the reproductive hymenium, with its 
protecting parts*. The polypoid and medusoid elements, how- 
ever, still continued to be treated as primarily independent or- 
ganisms, receiving each separate generic and specific names ; 
and indeed the time had not yet come when any other plan was 
practicable ; for the number of free Medusa-forms which had been 
traced to fixed polypoid forms was far too small to render possible 
any more philosophic system. 
Observations, however, gradually accumulated, and at length 
we became aware of a sufficient number of cases in which the 
connexion between the polypoid and medusoid elements was 
apparent to justify an attempt at combining the two in our 
classification. 
Accordingly we find, in an excellent and conscientious paper 
by M‘Crady+, an attempt made to combine the two elements 
in his arrangement of the so-called Gymnophthalmic Medusz. 
M‘Crady, however, gives a disproportionate prominence to the 
medusoid element, and in his nomenclature shows a tendency 
to adopt a more recent name by which the Medusa may have 
been known, rather than the older one under which the polypoid 
element has become familiar to us. 
Agassiz, in the fourth volume of his ‘Contributions to the 
Natural History of the United States, also shows himself im- 
pressed with the necessity of combining both elements, in order 
to allow of our forming an adequate conception of the Hydroid, 
while he gives no undue prominence to one of these elements 
over the other, and sees the justice of adopting for the entire 
Hydroid the name by which it was first systematically described, 
whether under the form of the free Medusa or of the fixed 
Polypite-colony. He has thus been frequently compelled to a 
dismemberment and a redistribution of existing generic groups, 
as well as to the construction of several new ones. Agassiz has 
here largely extended our knowledge of the Hyprorpa, and has 
made an important advance to a philosophic classification of the 
group; but I cannot admit that he has always made a correct 
estimate of the value of the characters which he employs in the 
construction of his genera, while he more than once overlooks 
the just claims of existing names to adoption. 
The necessity of combming the two elements in our concep- 
tion, description, and classification of the Hydroida is also main- 
tained im a series of excellent papers published in the ‘ Natural 
* Dujardin in Ann. des Se. Nat. 1845. 
t+ M‘Crady, * Gymnophthalmata of Charleston Harbour,” in the Pro- 
ceedings of the Elliott Society of Natural History of Charleston, South 
Carolina, 1859, 
So 
ay 
