EUDENDRIUM. 331 



GONOSOME. — Spoeosacs developed from the body of the liydrantli at the 

 proximal side of the tentacles, or from the hydrocaidus. Male sporosacs polytha- 

 lamic, female sporosacs monothalamic. 



Ehrcnbcrg/ perceiving that the Tabnlaria of the eailier autliors inchuled more than one 

 generic form, proposed to distribute tlieni inider two genera. The dismemberment to which 

 the old genus Tubiilaria was thus suljjectcd must be regarded as an important step in the classi- 

 fication of the Hydkoida ; but Ehrenberg scarcely recognised the true grounds of the division, 

 for he based it on the simple or branched condition of the trophosome, leaving the simple forms 

 in the genus Tithularia, and bringing the ramified forms into a new genus, to which he assigned 

 the name of Eudendriiim. 



The characters thus selected are of minor value, and the genus Eudendrmm, as defined Ijy 

 Ehrenberg, included not only forms which are properly separated from Ttibularia, but also true 

 Tulidnria, such as Tuhularia larijnx. The celebrated Prussian microscopist, however, did not 

 allow the more important characters, such as those derived from the disposition of the tentacles, 

 entirely to escape him, though he merely pointed to them as possibly affording to future observers 

 grounds for further generic distinction. 



Van Beneden^ seems to have been the first who felt the necessity of restricting the genus 

 Uudendrium to such forms as had their tentacles arranged in a single verticil, and of restoring 

 to the genus Tuhularia those in which the hydranth is provided with two verticils of tentacles, 

 regardless of the simple or branched condition of the trophosome. 



Still later, Sars^ founded the genus Ferigonimus for certain species which continued to l)e 

 included in the restricted genus Eudendrium, assuming as his chief grounds of separation the 

 position of the gonophores, which he believed to be confined to the hydranths in the true 

 Eudendriums, but distriliuted along the stems and branches in Perif/onlmus. This character, 

 however, is of comparatively little value, a much more valid one being found in the form of 

 the hydranth, as was first distinctly shown by Dr. Strethill Wright. (See general remarks on 

 the genus Wriyldia, given above.) 



The gemis Eudendrium must now be understood as limited by the characters assigned to it 

 in the diagnosis just given. All the species hitherto discovered are ramified, and there are no 

 hydroids on which the plantdilce {)hysiognomy is more decidedly impressed than we find it to be 

 on the various species of this beautifid genus. 



The peculiar form of trophosome described above in the generic diagnosis has as yet becu 

 found associated with only one form of gonosome. Until, therefore, some new observations sluall 

 come to invahdate our generalization, we shall be justified in referring any trophosome with the 

 characters above enumerated to the genus Eudendrium, whether the gonosome be kuoivn or not. 



This is in strikhig contrast with certain other hydroid trophosomes, such as the coryuoid 

 trophosome, which may belong to at least three genera, and that of Periijoniriius, which, as we 

 have akeady seen, may also have such different forms of gonosome associated with it as to render 

 it impossible, without this last element, to decide on the genus of the hydroid. 



1 " Coralleuthiere," ' ,Vbliaudl. der Berlin. Alcad.,' 18.33, p. 297. 

 " ' Recherches sur I'Erabrvogenie des Tuliulaires.' 

 ^ ' Fauna lit. Norveg.,' Erste Liefer, p. 8. 



43 



