m 



der udgaar fra Hydranthens atVundedii Basis, eller endelig 

 3) rodforniig tilsj^idset og besat med tine Heftetraade. De 

 to første af disse Former for Hydrorhiza forudsætter et 

 nogenlunde fast Underlag, medens de Arter, der har den 

 tilspidsede Rod med tynde Heftetraade, sandsyidigvis findes 

 staaende i blod Sandbund. 



Hvad Myrioihelas Struktur og Udvikling angaar, saa 

 viser de — efter Alhnans (l(i) og Korotneffs (72 — 73) ind- 

 gaaende Undersøgelser, — mange Eiendommeligheder. 

 Disse Undersøgelser gjælder Arten J/. cocksii, der i væsent- 

 lige Punkter afviger fra de øvrige Arter, — saaledes ogsaa 

 ved Besiddelsen af de eiendommelige ,.claspers" (AUman 

 [16]), som spiller saa stor Rolle nnder denne Arts Udvik- 

 ling, men som aldeles ikke forekommer hos de øvrige Arter 



— og Eesultaterne kan derfor ikke uden videre betragtes 

 som gjreldende hele Slægten. 



Det Materiale, jeg har liavt til min Eaadighed, har 

 ikke været egnet til histologiske Undersøgelser, og de Op- 

 lysninger jeg kan give om Arternes finere Struktur, er der- 

 for kun spredte og meget ufuldstændige. 



Hvad Eldodermen angaar, saa har den hos en Art, 

 M. itiitru. en meget eiendommelig Struktur, som jeg tid- 

 ligere har omtalt (29), men uden at give nogen Afbiklning 

 af den. Ektodermen bestaar hos denne Art af to tydelig 

 adskilte Lag, (Tab. V, Fig. 3 b), inderst et flercellet Lag, 

 der kun tarves svagt af Boraxkarmin, og udenfor dette sees 

 et Lag af Oylinderepithelceller, der imidlertid ikke ligger 

 parallelt med Stottelamellen, men som Inigter sig ud og ind. 

 Hydranthens Overflade dannes saaledes af en Mængde Ek- 

 todermpapiller, saa tætstillede, at man ved en Ectragtning 

 af Dyret meget vanskelig vil opdage, at dets ydre Flade 

 ikke er ganskejevn og glat. Jeg har ikke kunnet finde den 

 samme Struktur hos nogen af de ovrige Arter (Fig 6 viser 

 et Snit af M. i>]iri/gia); og det fortjener at bemerkes, at 

 denne eiendommelige Strnktur af Ektodermen forekommer 

 hos en Art, der — i Modsætning til alle de øvrige Arter 



— fuldstændig mangler Bedækningen af Tentakler. 



Entodernwn er overalt sterkt foldet og danner en 

 Række tætstillede, langsgaaende Kamme, af 2 — 3 mm.'s 

 Høide, der rager ind i Hydranthens Hulrum. 



I Tentaklerne og specielt i de Traade, hvormed nogle 

 Arter fæster sig til Underlaget, har Stottelamellem naaet 

 en ualmindelig Udvikling. Mod disses distale Ende tiltager 

 den nemlig voldsomt i Tykkelse, saaat den danner en chi- 

 tinøs Plade mellem Tentakelens to Cellelag, der i Tykkelse 

 overgaar Summen af disse (Tab. ITL Fig. 5). 



Alhnunn liar (Hi) givet en udforlig Fremstilling af 

 MijriotJielas Udviklingshistorie, og han er af den Opfatniug, 

 at Generationscellerne oprindelig skriver sig fra Entodermen. 



Korotiieff var ogsaa forst af samme Mening, og han 

 udtaler (72) : „De store embryonale Celler, der findes ved 

 Grunden af Blastostylernes Entoderm, ophoher sig paa 

 forskjellige Steder, deler sig, og danner en agglomeration-, 



Den norske Nordhavse-vpeditinn. Kristine B.ninevic: Hydruid:i. 



covoring, or 2) in the form of tentaculate attaehing fila- 

 ments, springing from the roiinded base; of the hydranth, 

 or 3) with a root-liko point, beset with fine attaehing tila- 

 ments. The first two of these forms of hydrorhiza pre- 

 suppose a somewliat firm suli-stratum, while the species 

 with tile pointed root aud tine attaehing tilaments wiil 

 probably be found on a soft sandy ljotton\. 



As regards the structure and development of Myrio- 

 tlida, it appears from Alhuan^s (16) and Korofneff't< (72, 

 73) minute investigations that they present many ])('culia- 

 rities. These investigations liad reference to the species 

 M. cocksii, which dififers in s(nne essential points from the 

 other species, as, for instance, in tlie possession of the 

 l>eculiar ..claspers"' (Allman [16]), which play so great a 

 part in the development of this species, but which are 

 altogether absent in the other species. Their result cannot, 

 tlierefore. as a matter of course be regarded as applicable 

 to the whole genus. 



The collection that I liave liatl at my disposal was 

 not adaptcd to liistological investigatioii. and whatever in- 

 formation I can give as to the more delicate structure of 

 the species, is therefore only fragmentary and very in- 

 completc. 



The edoderm is in one species, M. mitra, of a very 

 peculiar structure, as I have previously mentioned (29), 

 but without giving any illustration of it. It con.sists of two 

 distinct layers, (Pl. V, fig. 3 b), the inner being a multi- 

 cellular layer, only faintly tinged by borax-carmine, the 

 outer, a layer of eylindrical epithelium cells. The latter, 

 • however, does not lie parallel with tlic struetureless lamella, 

 but bends in "and out. The surface of the hydranth is 

 thus formed of a nundjcr of ectoderm papillæ, standing so 

 close together that on looking at the animal, its external 

 surface appears to be quite even and smooth. I have been 

 unable to discover a similar structure in any of the other 

 species (fig. 6 shows a section of M. phri/rjiu), and it is 

 worthy of reniark that this peculiar structure of the ecto- 

 derm occurs in a species which, unlike all the other species, 

 is entirely destitute of tentacles. 



The endoderin is wrinkled all over, forming a serried 

 row of ridges, 2 or 3 mm. in height. iirojecting into the 

 cavity of the hydranth. 



ln the tentacles, and still more in the filaments witli 

 which some species attach themselves to the sub-stratum, 

 the struetureless lamella has attained an unusual degree 

 of development, increasing enormously in thickness towards 

 their distal end, so as to form between the two cell-layers 

 of the tentacle a chitinous lamina which exeeeds in thick- 

 ness that of the two cell-layers combined (Pl. III, fig. o). 



AUii/itn (16) has given a full account of the develop- 

 ment of MjirioiJicla. and he is of oi)inion that tlie genera- 

 tive cells originate in the endoderm. 



Korotneff also shared this opinion at first, and says 

 (72): „The large emln-yonie cells found at the base of 

 the endoderm of the blastostyles accumulate in various 

 places, divide and form an agglomeration, which, as it 







