THE SUB-ORDER TUBULARIA. 



287 



Eudendrium has a species forming pretty little tree-like shapes in rock pools near low water 

 spring tides on the southern coasts of England. It * is about three-quarters of an inch in height, 

 and consists of rootlets and a stem 

 with regular branches, and has the 

 nutritive and generative zooids on it. 

 The outer tissue, or perisarc, is dis- 

 tinctly marked with rings, and is annu- 

 lated, and there are about twenty ten- 

 tacles, some looking upwards and others 

 downwards. The gonosome has male 

 and female sacs in whorls, and they 

 are placed just behind the tentacles or 

 on the stem lower down. Some small 

 medusae of the genus Lizzia belong to 

 this group. 



A third genus is Hydractinia, and 

 it is remarkable for its resemblance to 

 Millepora, one of the Hydrocorallinse, 

 but it is without the hard calcareous 

 base of this last. 



LIZZIA FLOATIXO HEXEATH THE SURFACE. 



Hydractinia has several species, and it was at first taken to be 

 a Bryozoon, from the horny spinous crust which it forms on the 

 surface of empty univalve shells. It forms numerous colonies, and 

 the hydranths are claviform, and arise from the surface of the 

 common base, or hydrophyton. There is a crown of tentacles, 

 which are filiform, and it encircles the conical mouth. The genera- 

 tive buds are on smaller polypes, which are without mouth, and 

 end in globular clusters of thread cells representing the tentaclea 

 of the hydranth. The generative buds cluster around this polype, 

 c which is called a blastostyle, and some contain, around a central 

 body, the ova, and others the male elements. 



A common species (Hydractinia echinata) is found on the 

 es of England, France, and Belgium, and covering more or less 



JSVJIJ.E:NIJ.KIUM. IMSIOXE. (AitirA.um.an.) . , T , , 



A, coi,my. natural siz,> ; B , male colony, masni- dead urn valve shells inhabited by Hermit crabs, it has, near the 



Hod ; o, female bearing gonophoreB, luagDined. , ,.,... , i 



margin of the base, spiral appendages, cylindrical in shape, and 

 very contractile and movable. They twist and untwist with great vivacity. 



The genus Podocoryne is not very unlike the last mentioned, but all the polypes are tentaculate. 



soir.a, body). The buds which produce the medusae, or the generative part of the colony, are tho Gonosome (Greek, f/onos, 

 offspring). When the Trophosome branches, or has offshoots, each one is a zooid, and the proper nutritive zooid, which has 

 a mouth and digestive cavity, is the hydranth (Greek, hydra, hydra ; anthos, flower). The mouth is at the end of a cone, 

 which is called the hypostome (Greek, hypo, under ; stoma, mouth). The common basis of the Trophosome, by which the 

 zooids are connected, is the hydrophyton (Greek, phyton, a ulant), and the end of the hydrophyton, or root, is the hydro- 

 rhiza (Greek, rhiza, a root). All the hydrophyton between the root and the hydranth is the hydrocaulus (Greek, kaulos, a 

 stem). The bud, or zooid, which contains the reproductive elements, is a gonophore (Greek, yonos, offspring ; phorco, I 



A planoblast (Greek, plftnos, wandering) is a generative bud, fit for a free locomotive life ; and a blastostyle (Greek, 

 stylos, a column) is a columniform zooid, destined to give origin to generative buds. Umbrella is a term for t 

 gelatinous bell of a medusa ; the manubrium is the part carrying the mouth ; and the velum (a veil) is a membranous 

 perforated diaphragm, which stretches across the orifice of the umbrella which communicates with the external water. 



* Eudmdrium insigne. 



(*ur Ail man . } 



