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REPORT ON THE HYDROIDA. 15 
were it not for their unbranched condition, they would closely resemble the phylactocarpal 
appendages of Cladocarpus pectiniferus of the present Report. I have here taken for 
granted that the entire structure is, as interpreted by Mr. Fewkes, a modified branch rather 
than a hydrocladium, though the fact which he mentions of its carrying along its proximal 
portion, which forms a kind of peduncle for the phylactocarp, a series of hydrothece 
presents a difficulty in the acceptance of this view. Mr. Fewkes does not give a 
magnified figure, and it is possible that what look like hydrothece are really only large 
cauline nematophores. 
Ramification. 
The Plumularidze present considerable differences in the details of their ramification. 
What may be regarded as the typical ramification in both the great sections of the 
Plumularide shows itself in a simple or branched stem, from two opposite sides of which 
the ultimate ramuli or hydrocladia are given off. These ramuli are thus disposed in a 
regularly pinnate manner, and give to the colony the elegantly plumose aspect by which 
the designation of the typical genus has been suggested. In most species the pinne are 
alternate, but in a few, as in Plumularia catharina, for example, they are opposite. 
In some rare cases the hydrocladia are confined to one side of the stem (Monostachas 
dichotoma of the Gulf Stream exploration!). In Streptocaulus pulcherrimus of the Chal- 
lenger (Pl. XVI. fig. 1), they are disposed in a continuous spiral along a simple stem. 
Here, however, the hydrocladia really spring from one side only of the stem, and then, 
by a revolution of the stem round its axis, the lower end remaining fixed, the hydrocladia 
are thrown into the beautiful spiral characteristic of the genus. In Antennularia antennina 
of the European seas the hydrocladia are disposed in regular verticils round the stem, 
while in other species of Antennularia (Pl. IV. figs. 5, 6), the verticillate arrangement 
gives place to a scattered one. In Sciwrella indivisa (Pl. V.) they are in four longi- 
tudinal alternating series. In Hippurella*® they are pinnately disposed on the proximal 
portion of the branches, but distributed on all sides towards the distal extremities. In 
Antennella no proper stem is developed, and the hydrocladia are borne directly by the 
hydrorhiza. 
The main stem may be quite simple, or it may be more or less branched. In the 
latter case the ramification is usually irregular, but it is sometimes regularly dichotomous 
(Monostechas dichotoma). In some cases, as in Lytocarpus spectabilis (Pl. XV.) and 
Aglaophenia macgillivrayi (Pl. X.), the stem gives off branches, which, though destitute 
of hydrothec, are disposed in perfectly regular pinne, These primary pinne give 
support to the true hydrotheca-bearing pinne, and the ramification thus becomes doubly 
1 Hydroids of the Gulf Stream, p. 37, pl. xxii. figs. 1-5. 
* Hydroids of the Gulf Stream, p. 86, pl. xxi. figs. 7, 8. 
