32 



Under Nordh.-Exp. er Mi/riothela-Årtevnes Aiital for- 

 øget, og on Saramenstilling af alle Arter giver det Indtryk, 

 at M. cocksii danner en Grænseforni, der antyder, ad 

 hvilken Vei en Corijiie har kunnet udvikle sig til en Mijrio- 

 fhela. Har man f. Ex. en Form som C. gigantea^, men for- 

 grenet, istedenfor som denne at være solitær, saa kan man 

 tænke sig Overgangen til M. cocksii skeet ved, at alle Hy- 

 drantlier paa en nær atrophieres, gaar over til at være 

 Blastostyler, medens den ene Hydrantii kun staar i Ernæ- 

 ringens Tjeneste. Disse Overgangsformer mangler imidler- 

 tid fuldstæ-ndig. og jeg tinder Spranget saa stort, og J///- 

 riothela- Arternes Eiendommeligheder saa sterkt udviklede, 

 at de bør staa som en egen Familie. 



Wncliss Sammenligning af 2Ignofliehl med en Koloni 

 af Hgdradinia bringer den Tanke nær, at man hos Mgr?- 

 othela har en Rhizocaulomdannelse, i Lighed med hvad 

 man tinder hos Perigonimiis og Lafoikt, og at Blastosty- 

 lerne udgaar fra Rhizocaulomet istedetfor som hos Hgdrac- 

 iinia at udgaa fra den^krybende Hydrorhiza. 



En nærmere Undersøgelse af Myrwthelas Entoderm 

 har imidlertid vist. at den fordoiende Hulhed fortsætter 

 udcn Afln-ydelse lige til dens Basis og at Strukturen er 

 fuldstændig den samme ogsaa i den nederste Del. der bærer 

 Blastostylerne, og dette har bragt inig til at betragte det 

 hele som en eneste Hydranth. At Blastostylerne har sin 

 Plads paa selve Hydranthen er en Eiendomnielighed, som 

 vi træffer endnu mere udpræget hos TithitJariderne, idet de 

 her har sin Plads indenfor Kredsen af de proximale Ten- 

 takler, og er omdannede i en saadan Grad, at man vanske- 

 lig vil crkjeiuie dem som Blastostyler, hvis man ikke liavde 

 en Ra'kke af Mellemled der viser deres Oprindelse. 



(t. O. Sårs foreslaar, at den liritiske Form skal be- 

 liolde navnet Cocl-s/i, det Artsnavn, den lik af sin Ol)dager 

 Vignrs. Senere (105, Anm.) foreslaar han ogsaa at stille 

 de to oprindelige Arter i hver sin Slægt, Myriothéla (Sårs) 

 og Spadix (Gosse), et Forslag, som jeg ved min forcløbige 

 Meddelelse gav min Tilslutning. Efter den Tid har jeg 

 imidlertid undersogt et stort Materiale Hydroider og ved 

 Betragtning af de Variationer. som forekommer indenfor 

 Slægter af andre Familier, er jeg kommen til det Resultat, 

 at forskjellen mellem de to Arter ikke er saa indgrijjende, 

 at den berettiger deres Adskillelse i forskjellige Slægter. 

 Blandt de Hydroider jeg har havt til Undersøgelse, tindes 

 mindst 4 nye Arter af Slægten, og vi har altsaa nu: 

 Fam. MyrlofJielidne represeuteret ved 1 Slægt, ilyriothela, 

 inden hvilken der kjendes 6 forskjellige Arter. 



Fælles for disse Arter- er det. at de fuldstændig 

 mangler Hydrocaulus, dermed ogsaa Perisarc, og at Bla- 

 stostylerne har sin Plads paa Hydranthens nederste Del. 

 Deres Hydrorhiza optræder under tre forskjellige Former, 

 enten 1) pladeformig udbredt paa Underlaget, med cbiti- 

 nost Overtræk, eller 2) som tentakelforniige Heftetraade, 



' Se Pag. IJ, og- Bonnevie „Neiie norwegishe Hvdroiden-', IS98. 

 - Undt. muligens M. cocksii. 



During the N. Atl. Exp. the number of species 

 has been greater, and througli a comparison of all the 

 species it seems, that 2J. cocksii stands as a transition-form, 

 indicating the way in which a Coryne form has been able 

 to develope into a Myrioilieln. If, for instance, we have a 

 form like C.gigardea''-, but ramified instead of being solitary 

 as the latter is, ^\;e can iniagine the hydranths but one being 

 atropbied, and turning into blastostyles, while the one 

 hydranth only acts in the service of nutrition. These tran- 

 sition-fornis, however. are altogether wanting. and I con- 

 sider the Ijreak to be so great, and the peculiarities of 

 the Myrioiliéla species so highly developed. that tliey ought 

 to stand as a separate family. 



Hi\iclcs's comparison ot MyriotJiela with a colony of 

 Hydracti)iia suggests the thought that in Myriothda we 

 have a rhizocauloni formation similar to that found in 

 Perigoitimus and Lafoi-a. and that the blastostyles spring 

 from the rhizocaulom instead of, as in Hydrdctiuia, from 

 the creeping hydrorhiza. 



A closer examination of MyriothélcCs endoderm, how- 

 ever, has .shown that the digestive cavity continues without 

 interruption right to the l)ase, and that the structnre is 

 exactly the same in tlie lnwer portion, whicli bears the 

 blastostyles; and this has led nie to consider the whole as 

 a peculiarity tiiat we meet with in a yet more marked 

 degree in the Tiéidaridæ. as there they are within tlie 

 circle of ])roximal tentacles, and are transforraed to such 

 an extent, that it would be difticult to recognise them as 

 blastostyles. if there were not a series of intermediary 

 links which show tlieir origin. 



Prof. G. (}. Sårs suggests that the British form sliall 

 retain the name cochsii, the specitic name it received from 

 its discoverer Vigiirs. Subsequently (105, note), he suggests 

 l^lacing the two originally known species each in a separate 

 genus, as Myriothela, Sårs. and Spadiæ. Gosse. — a pro- 

 posal I supported in my preliminary account (29) of some 

 of the X. Atlan. Exp. species. Since tliat time, however. 

 I have examined a large numlier of hydroids. and on con- 

 sidering the variations which occur within genera of other 

 families, I have come to tlie conclusion that the differeuce 

 between the two species is not so important as to justify 

 their division into different genera. Among the hydroids 

 I have examined. there are at least 4 new species of tiie 

 genus, and we have now, therefore, Fam. Myriotliclidae, 

 represented by 1 genus, Myriothela, in which 6 difierent 

 species are known. 



As characteristics comraon to all tliese species^ Ave 

 have, tirst, the total absence of hydrocaulus, and with it 

 the perisarc, and second, that the blastostyles are situated 

 on the lower portion of the hydrantii. Their hydrorhiza 

 makes its appearance in three different forms, 1) lammelli- 

 formly expanded on the sub-stratum with a cliitinous 



' See p. l.'i, iinil Bunnevif ,.Xeue norwegisclie Hvdroiden-, IS!),". 

 - Except perhaps M. cocksii. 



