REPOKT ON THE HYDROIDA. 15 



were it not for their unbranched condition, tliey would closely resemble the phylactocarpal 

 appendages of Cladocarpus pectiniferus of the present Eeport. 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 phylactoearp, a series of hydrothecse 

 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 hydrothecse are really only large 

 cauline nematophores. 



Ramification. 



The Plumularidae present considerable diflferences in the details of their ramification. 

 What may be regarded as the typical ramification in both the great sections of the 

 Plumularidse shows itself in a simple or branched stem, from two opposite sides of which 

 the ultimate ramuli or hydrocladia are given ofi". 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 t3rpical genus has been suggested. In most species the pinnae 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 {Monostcechas 

 dicliotoma of the Gulf Stream exploration ^). In Streptocaulus pulcherrimus of the Chal- 

 lenger (PI. 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, 

 l)y 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 Antenmdaria antennina 

 of the European seas the hydrocladia are disposed in regular verticils round the stem, 

 while in other species of Antenmdaria (PI. IV. figs. 5, 6), the verticillate arrangement 

 gives place to a scattered one. In Sciurella indivisa (PL V.) they are in four longi- 

 tudinal alternating series. In Hipiyui'dla "- they are pinnately disposed on the proximal 

 portion of the branches, but distributed on all sides towards the distal extremities. In 

 Antennella no jjroper stem is developed, and the hydrocladia are borne directly by the 

 hydrorhiza. 



The main stem may be quite simple, ov it may be more or less branched. In the 

 latter case the ramification is usually irregular, but it is sometimes regularly dichotomous 

 {Monostcechas dicliotoma). In some cases, as in Li/tocarpus spectahilis (PI. XV.) and 

 Aglaophenia macgdlivrayl (PL X.), the stem gives off branches, which, though destitute 

 of hydrothecse, are disposed in perfectly regular pinnse. These primary pinnse give 

 support to the true hydrotheca-bearing pinnae, and the ramification thus becomes doubly 



1 Hydroids of tlie Gulf Stream, p. 37, pi. xxii. figs. 1-5. 

 " Hydroids of the Gulf Stream, p. 36, pi. xxi. flgs. 7, 8. 



