272 HYDROID^. Part IV. 



a full account of them hei'e.^ The head of this Hydroid is capahle of assuming 

 a great variety of shapes; but most frequently, especially when the animal is in its 

 native haunts, it assumes an extremely extended condition, with its crown of tenta- 

 cles, the proboscis and buccal tentacles, and the bunches of medusoids stretclied 

 to the utmost (PL XXIII. Fig. V')} The buccal tentacles, when fully extended 

 (PI. XXIII. Fig. V\ i), are as long as the proboscis (/>) from the base to the mouth, 

 and very slender and tapering ; yet they may at another time be so contracted as to 

 resemble mere protuberances, hardly, if at all, longer than broad (PI. XXII. Figs. 19 

 and 2.3, f). Between these two extremes there are all grades of length and 

 breadth, as may be seen by referring to our figures. The lower circle of tentacles 

 presents as great a variety of attitudes as the upper one. When the tide flows 

 rapidly, they are ysually stretclied out in the direction of the current, and seem 

 to imdulate with every passing ripple ; in still watei', however, they are more 

 active, and more apparently under the control of the animal. At one time they 

 are thrown upwards, with a sudden sweep, as if to embrace an intrusive animal 

 (PI. XXII. Fig. 22, t), and quickly contracted, and then concentrated about the 

 mouth, along with the buccal tentacles [f)'. On such occasions they very frequently 

 become globular at the tips, so that they might readily be supposed to retain 

 this shape normally.^ At the next moment, perhaps, the captured creature, proving 

 to be unpalatable, is rejected with as much readiness as it was seized, by throwing 

 back the crown of tentacles {Figs. 25 and 28, t), and disclosing the interior of 

 the stomach (/*), with a sudden and sometimes often repeated gaping. Sometimes 

 the contractions of the proboscis {Fig. 26, y) are so vigorous, and the buccal 

 tentacles {f) are laid together so evenly and compactly, that the whole is reduced 

 to the smallest possible space, with nothing to indicate the presence of the tactile 

 organs, but the longitudinal ridges, which extend nearly down to the disk. Again, 

 the larger tentacles, retaining their taper points, simply shorten and thicken trans- 

 versely {Fig. 20, t), and, turned either inwards or outwards {Fig. 19, t), retain a 

 fixed position, while the proboscis swells up into a globular shape {Fig. 20, a), 

 and at times constricts into two more or less distinctly-defined portions {Fig. 19, 

 a h). In this last phase the hydroid appears to be in a highly irritated state, 



1 Tlie two species of Thainnocnidia, Th. spec- the animal was in an upright position, in order 



tabilis and tenella are identical in every respect, to allow the bunches of medusoids to fall back 



excepting size and tlie mode of branching, the latter from the proboscis. 



species being considerably smaller than the former, ^ If thrown into alcohol in this condition, tliey 



and branching very openly and loosely, and there- would very naturally be described as club-shaped, 



fore the illustrations of one will be used recipro- if they w^re studied from preserved specimens 



cally for the other. alone, as may happen in case of specimens brought 



^ The figure here referred to was drawn while home from distant expeditions. 



