THE PLUMULAKIDvE. 35 



hydrocladia, as in the young pseudo-corbula, with ordinary hydrocladia alternating with the, 

 protective branchlets a condition not found in the fully developed structures of the species 

 examined (L. clarkci). In Lytomriin* xpn-tnliilin Allman this seems to be the normal state of 

 affairs, the hydrocladia and protective branchlets being intermingled along the stem. 1 In all species 

 of Lytocarpm the phylactogonia are morphologically hydrocladia and not appendages to hydro- 

 cladia. When these are aggregated together on one portion of the branch to the exclusion of 

 the true hydrocladia, a pseudo-corbula is formed; but when they are not thus aggregated the 

 gonangia are protected by the individual phylactogonia to which they are attached. 



Phylactocarps which are, morphologically, appendages to the hydrocladia are found in the 

 genera Cladocarpus, Aglaophenopsis, and RtreptocuHlux. In Cltuloctirpnit this appendage springs 

 from the hydrocladium immediately below and to one side of the proximal hydrotheca. Two very 

 distinct types of phylactogonia are found in this genus. In one, typified by 6'. Jlc.rilin Verrill 

 (Plate XXVI, fig. 12), the gouaugia are, borne on the stem near the phylactogoninm which is 

 branched much like a stag's horn and arches over the front of the stein, those from opposite sides 

 alternating, but still interdigitating to a certain extent, so as to conjointly form an excellent 

 protection for the gonangia over which they extend. The number of branchlets into which the 

 individual phylactogonium is divided varies from two to live or six. The other type is well 

 shown in Cladocarpus j><n- ilium (Plate XXVIII, fig. 7). Here the phylactogonium consists of a 

 straight central shaft, which usually shows indications of internodes, each of which gives off a 

 short branchlet and bears a gonangiuin. In ('. i>ourtlc$!its there are no branchlets, the phylacto- 

 gonia consisting of straight stems divided into iuteruodes bearing nematophores and gonaugia 

 (Plate XXIX, fig. 2). 



In AylHopJiciiopxi* the phylactogonium is supposed to be a greatly produced mesial nemato- 

 phore of the proximal hydrotheca. For reasons already stated it is impracticable to insist in all 

 cases on such homologies. In the three species of this genus furnishing sufficient material for 

 investigation, the phylactogonia have one or more hydrotheca- on their distal ends or throughout 

 their extent. This is, I believe, 111114116 among the Statoplea, and if consistent would prove an 

 excellent generic character. The, gonangia in this genus, as in Cladocarpus, are borne on the stem 

 in some species (A. Itirxtittt, Plate XXIX, fig. 11') and on the phylactogouia in others (A. rerrilli, 

 Plate XXX, fig. :!). 



The remaining phylactocarpal genus of the Statoplea is Stnytocititlux. The gonosome was 

 unknown to the original describer of this genus (Allman), but was afterwards (bund by Quelch in 

 specimens taken from the cable off the Gape Verde Islands. 2 In the single species known the 

 phylactogonia spring from the side of the mesial nematophore of the proximal hydrotheca and 

 resemble greatly the structure in Gladocarpus pourjalesius, being straight, unbrauched, jointed, 

 and bearing nematophores and a gonangium on each internode. 



This author has the following to say concerning phylactocarpal and gymnocarpal forms: ; 



SchizotriclM has been referred by Pro!'. Alliiiiin to the section liiimnoi-iirpn of the Eleutheroplea, anil Clado- 

 carpus to the section riiylaclunirpii of the Statoplea; and. .induing on the point of function us to whether the repro- 

 ductive appendages of the hydrorladia on which the gonotbeca- are placed are or are not protective, the genn,-, 

 Hreptocaiilus must be removed from the Phylactocarpal Statoplea, among which it was temporarily placed, to the 

 section (iymnomrpa. < In the other hand, since the reproductive appendages and segments which bear the gonothec;e 

 seem in the three cases to be strictly homologous, and thus but rudimentary or varying forms of the phylactocarp, 

 it seems necessary, if the terms tiymnocarpu and 1'hijlactocarpti are to be retained with any detinite meaning, that 

 all three genera should be placed among the phylactocarpal forms. 



The present writer agrees entirely with the latter part of this quotation. Form is of greatly 

 more importance than function in systematic work, and while it is doubtless true that the phylac 

 tocarpal appendages of tifn-ptoctniluii and several other forms afford little, if any, protection to the 

 gonaugia, their morphology is such that they must be regarded as structures associated more 

 closely with the gonosome than with the trophosome, and they can be most conveniently discussed 

 by using the terms phylactocarpal and gymnocarpal. as originally suggested by Allman. 



~ ' Report on the Hydroida dredged by II. M. S. Challenger during the years 1873-76, Pt. 1, Plumnlarida-, 1883, 



pi. xv, fig. 4. 



- Oil some deep-sea and shallow-water llydrow.a, Annals and Maga-cine of Natural History, 5th ser., X\ I, L885,p.l. 



"Idem., p. 13. 



