Australian Hydroids. ;351> 



eggs (pathological) smooth, with a ,small projection at the distal 

 pole. Colour, oiaiige-biown to deep olive-green. 



H. attenuata Pallas. — Brauer says that this is Kosel's " straw- 

 yellow polyp," that it has never been found again, and that it is. 

 probably only a colour-variety of //. viUgaris. Brauer strangely 

 overlooks the remarks of Johnston, who observed, this form. He 

 says: " Ihis, which is represented very exactly in the plates of 

 Rosel's beautiful work, is a larger animal than U. vidgaris, and 

 comparatively rare, less sensible to external impressions, and of a 

 more gracile form. Its colour is a dilute olive-green, with paler 

 tentacula, which are considerably longer than the body, and hang, 

 like silken threads in the water waving to and fro without assum- 

 ing that regular circular disposition which they commonly do in 

 the H. viridiis.'' Hincks, liowever, like Brauer and Bedot, thinks- 

 is is probably a variety of //. vulgaris. Syn. — H. palleiis Lin. 



H. hexactbiella von Lendenfeld. — Von Lendenfeld describes the 

 body as perfectly cylindrical, and 15 mm. in length, while the 

 tentacles when fully extended, are said to reach only 5 mm. The 

 body is colourless, and there are two sorts of nematocysts. *^ It 

 can be distinguished from other Hydras by the constancy in the 

 number of arms, which is invariably six. These tentacles are all 

 equal in length and thickness, and the angles between them are per- 

 fectly equal, measuring 60°. Such regularity has been observed 

 in no other species. It appears that in this respect our Hydra is 

 more highly developed than the others, as the number of antimeres- 

 has been defined." 



The " stalked " condition referred to in these descriptions is not 

 a permanent character, but is merely a distension resulting from 

 recent feeding, Avhich affects only the upper part of the body, so 

 that the lower part has by comparison a stalk-like appearance. Tlie 

 young Ilydra^ so long as the body-cavity ccmnnmicates with that 

 of the parent, assumes a similar form when food has been taken 

 by the latter. Ihis differentiation of the alimentary tract, prac- 

 tically into stomach and intestine, marks a higher stage of d.evelop- 

 ment than that attained by such forms as H. viridis. 



Jickeli, in his paper on Uydra^ figures tlie four diflVrciit foiins- 

 of nematocysts found in the genus. First we have the large form, 

 which has a stout ovate capsule, truncate at the smaller end, with a 



1 C. V. .lickeli. Ueber deii hiHt.iolojfiaclien \\i\u von Kudeiulriiini Khrb. tuid Hi/dra L. 

 Morpholo^'. .J.ibrb., M. viii., p. 373, T. wiii., fi;;s. 1 :{. (In fi;f. 3 the letterinjf is evidently wronjr,. 

 the letters ^ and y— called b and c in the text— should be tran.sposed). 



