32 AMERICAN HYDRO1DS. 



Among the Bleutheroplea the genera Schizotricka, Diplopteron, Polyplitmularitt, Hippurella, 

 and Callicarpa are here regarded as phylactoearpal, the remaining geiiera Plumularia, Monothecn, 

 Antennularia, Antennopsis, Galvinia, Anteniu-lld, and Monosttvchas being gymnocarpal. 



Although it is contrary to the position taken by previous writers, several of these genera, such 

 as Sclnzotrwlia, Diplopteron, and Potyplumularia are, as above indicated, regarded as phylacto- 

 earpal. The reason for this is as follows : In examining a series of Schizotricka dichotoma collected 

 in the, West Indies, I found evidence sufficient, in my opinion, to show that the branching of the 

 hydrocladia is a character directly associated with reproduction; in other words, it is temporary, 

 often connected more intimately with the gonosome than with the trophosome, and is designed for 

 the protection of the gonangia (Plate XV, fig. 1). In mature specimens the hydrocladia are bifur- 

 cated near their bases, one portion, which 1 regard as the hydrocladium proper, continuing 

 unchanged with regularly disposed hydrothecse and nernatophores. The other portion, which I 

 regard as an accessory branch or phylaetogonium, is bifurcated a short distance above its origin 

 and one of the resulting branches is again bifurcated, making three ultimate branchlets to the 

 phylactogoninm. Upon the lirst, or nonbifurcated part, the gonangium is borne and some of the 

 hydrothecie are replaced by nematophores, while on the bifurcated part there are no gouaugia and 

 one fork has all but the terminal hydrotheca suppressed and replaced by numerous nematophores. 

 In a specimen with obviously matured gonangia the hydrocladia with their phylactogonia are 

 directed forward so that those from opposite sides almost touch each other. Thus the gonangia 

 are clasped, as it were, between the protective phylactogonia from opposite sides where they are 

 more or le-'s protected by a great number of nematophores. A specimen with immature gonangia 

 has the hydrocladia directed laterally, as usual among plumularians, while a colony without 

 gonosome from the same place and identical with the last in every other respect has the hydro- 

 cladia unbrauched and directed laterally, so that the specimen would, without doubt, be placed in 

 the genus Plhmulariii, had not other colonies with gonosomes been found. 



It seems evident, therefore, that the branching of the hydrocladia is a character associated 

 with the maturity of the colony, and that we have here a structure which represents in the 

 Eleutheroplea the protective branchlets of the genus Cladovarpm among the Statoplea, the main 

 difference being that the hydrotheca' are entirely suppressed in the latter case and only partially 

 so in the former. The fact that the hydrocladia are directed forward in sexually matured colonies 

 only is of considerable interest, and I am inclined to think that the same thing is true in certain 

 of the "Catharina group" of Phtmuluria, for example, Plumularia geminata Allman. It is alto- 

 gether probable that the accessory ramuli or branchlets with which the hydrocladia in Hchizotrieha 

 are furnished, are of the nature of gonosomal structures, and I therefore include this with the 

 following forms among the phylactoearpal Eleutheroplea. 



lu JHplopferon grand v (Plate XVI, fig. 2) we find a phylactocarp greatly resembling that fre- 

 quently met with in Cladocarpus. In this case the gouaugia are borne on accessory ramuli springing 

 from the bydrocladia and composed of three branches, each bearing numerous nematophores and an 

 occasional hydrotheca. This form of phylactoearp shows the intergradation between that structure 

 in Clndocnrpnti and Mchiztitricha. In Cladocurpus there are no hydrotheca' on the phylactogonia, in 

 Diplopteron there are a few, in Schizotricha dichotoma there are a still greater number, while in 

 S.parvula these accessory ramuli are apparently unmodified branches of the hydrocladia. We 

 thus find what appears to be a satisfactory demonstration of the homologous nature of branched 

 hydrocladia and phylactogonia. It must be borne in mind also that hydranths and sarcostyles are 

 homologous structures and often seem to be interchangeable in the economy of the colony, so that 

 the replacing of hydrotheca' by nematophores in the more differentiated phylactogonia is, after all, 

 a simple and natural process. 



Dr. J. Walter Fewkes discovered among the material secured by the Blake, iu 1878-1880, two 

 other remarkable genera of phylactoearpal Eleutheroplea. In Jlippurclla, (Fewkes not Allman) 

 ( Plate X VII, fig. 3) the distal end of the branch is highly modified for the protection of the gonangia, 

 the hydrocladia on this portion of the colony being apparently modified into a great number of 

 nematophorous branchlets arranged in whorls and curving upward over the gonangia placed iu 

 their axils. These branchlets or ribs are true phylactogouia and are without hydrotheca' although 

 they are, in all probability, modified hydrocladia. 



A still more specialized phylactocarp was discovered by l)r. Fewkes, and formed the basis of 



