THE SEliTUJ.AKID.i:. 5 



minimum just jriven. Mature specimens of I',isi/fli,<i </ mulriil, n f<it</. for instance, an- sometimes 

 less than one-fourth (if an inch in height. It must In- remembered, however, tliat height is not 

 necessarily a true criterion of the actual -i/e of the' colonies. [)r. Hull found a specimen of 

 .l/i/, limirni </''</<"//<" which consisted of .",.",0 shoots, aye-rapine; ' inches in length, estimated to 

 contain l.uoo.oeio individual hydranths.' 



'Hi, St,in.--\\\ by far the greater niimlpcr of Scrlularida- the stem U a perfectly simple 

 structure, be in"; monosiphonic (con>i-t in"; of a single tulie). composed <,f the normal hi-toloe'ical 

 layer.-, as found in the hydroids, divided into more or le-s regular internodes. The regularity of 

 the latter, however, is greater union"; (he 1'lumularida' than in the family under di>cii--ion. 

 There are l>ut two departures from this simple type of stem that are of sullicient importance to 

 demand attention here. These are 



(<i) The fascicled stem, as illustrated in S. ,-tiilin;ll,i </,/i//'. (Kijr. 1). This con-ists of an 

 a ".-<_; re Cation of (lilies that are closely adherent MI as to form a compound stem made up of 

 numerous tulics. There is a dillcreiicc, which we will lind to he more apparent than real, 

 between the fascicled stem as found in the Sertulariela- and that found in many I'himularida- and 

 discussed in the first part of this work (pp. I N. where there is a central or axial tube from 

 which arise all of the branches and a number of peripheral tube- that do not e-he- origin to 

 branches or h ydrocladia, ' and therefore it (tin- axial tube) has received the name " h vdrocladiale 

 tube." In X rliiliii-: Hi/ iimji this state of all'airs doe-s not ii/>j>- '/ to exist. On I he contrary, the 

 brunches seem to arise from almost any of these tubes which compo>e the fa-cicled stein. In li";. 1 



we have a porti f the stem which has I n boiled in potash to loosen ihe connection between 



the tubes /'// xi'fu. The upper part has been dissected with needles, so that the component tubes 

 are separated. It is readily seen that the brunches beunny; hydrotln-ca- ari-e from several of the 

 tubes instead of one. Sometimes these lube's seem to originate from one of the branches, as at ,/ 

 in the lie-lire, and puss downward, Divine; oil' another branch, as at /<. Au'ain. on,' of the- t ubes can 

 be traced for a Ion"; distance without ".h ini!- unv indication of branches An examination of the 

 point of attachment of this same specimen shows that the hydrorhix.a appears to be made up of a 

 continuation of these same tubes, \\hich simply separate to form individual rootlets. I ha\e 

 elsewhere : shown that these hydrocladia and hydrorhi/al elements an- homologous in the I'lumii- 

 hiridu', and the same thine- appears to lie true here, and in some instances it is perfectly clear 

 that the hydrorhi/al elements are modified hydrocladiu. 



A further dissection of this specimen, represented in \\<r. L'. (dearly reveals that this is con- 

 stantly true in >'. inii/i. \\\ carefully dissecting out the tube -/ / we find that it continues 

 downward through the stem and is bydrothecate tlirouyhoiit. altlioiie-h the hydrotheca' are 

 completelv co\ ered by the other tulies when in normal relation, beiny axial in the pol\ ^iphonic 

 stc'in. \\'e will therefore call it the axial tube. From the ba-es of the hydrothecffi on this axial 

 tube are u'iven oil' branches which pass ilownward in the form of tubes and in their normal 

 relations form the accessory or peripheral tubes of the fa-cirle.| stem. ( r'iir. -. ". -'). \Ve thus find 

 that the accessory- tubes are merely modified hydrocladia arising, as do the normal hydrocladia, 

 from the buses of the hvdrothec:e. Sonic of these accessory t lilies 1 1m- formed v.i\e origin to 

 other brunches lie-urine- liydrotheca- a hmy distance beloyv the actual oriu'in of the tube. 

 (Fie-. _'. ,.) It thus appears that all of the branches arise either directly Hie-, i'. I,) or indirectly 

 from the axial tube, the dill'erence beiny; that in the latter case they arise from accessory fcul 

 that are themselves really modified hydrocladia. 



This discovery is of yreat i -pholoL;-ical and s\stinnatic importance, bei-aiise it ^-jyes us a clue 



to the real oi-ie-in of the accessory or peripheral tubes, a matter not hitherto explained in a satis- 

 factory manner, so far as I knoyv. although I have found the same condition of affairs j (l t| H - 

 plmmilariaii Cladocarpus paradi&ea* and in a species of Ttecocarpus, but did not at that time see 

 the full significance of the fact. 



'('lark, Alaskan Hyln.i.ls. Is7i;, p. 230. 



- Tin- term " hyilnii-laili:i " a< applii-il t" the l'lninnlari.l:i si-_'iiilii-.< tin- ultimate lu-aiu-lie.s \\ hirh liear the liyilni- 

 tlicc.-i-. It is not ordinarily used in n.nnrrtinn ilh c.lhc-r ._!.. tips. 



'See Part I. p. 7. 

 1 See Part I, p. 6. 



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j LIBRARY 



