862 " THETIS " SCIENTIFIC RESULTS. 



are all similar, somewhat rectangular in shape, the upper corners 

 of the rectangle being, as it were, clipped off so that the sarco- 

 styles may issue by a ])air of apertures. The hydroclades are 

 divided into long regular internodes not more than seven in 

 number, the greater part of each of whicli is occupied by a 

 hydrotheca. The lower portion of an internode slightly over- 

 arches the hydrotheca of the preceding one, and the whole cavity 

 is divided by very numerous (eleven to thirteen) septal ridges, 

 two of which lie proximal to the hydrotheca. 



The hydrotheciB are tubular, extremely deep and narrow, about 

 four times as long as wide, approaching in this respect the bizarre 

 Cladocarpis tenuis, Clarke. Their anterior profile is somewhat 

 S-shaped, narrower at the middle, a long inward curve dividing 

 the hydrotheca into two portions, and giving rise to the specific 

 name signifying " long-waisted." The margin of the hydrotheca 

 is horizontal and is furnished with a single, anterior, flame- 

 shaped tootli, the remainder being very minutely and irregularly 

 crenate. Across the base of the hydrotheca, stretching from the 

 lower end of the posterior wall to a minute knob of chitin on 

 the anterior wall is a chitinous septum perforated to allow the 

 passage of the cffinosarc which connects the hydrantli with the 

 common coenosarc of the colony. On the hydrothecal side this 

 opening is guided by an offshoot of the basal septum which forms 

 a short tongue of chitin bending over it, and resembles a 

 diminutive intrathecal ledge (PI. Ixxxix., fig. 7). 



The sarcothecse are characteristic when mature. The supra- 

 calycine are large, and for almost half their height overtop the 

 margin of the hydrotheca. In all cases, they possess two 

 apertui'es, one terminal, the other latero-adcauline (PI. Ixxxix., 

 fig. 7). Frequently, however, the terminal aperture has lost its 

 general circular shape, and has become elongated, exactly 

 resembling that of the sarcothecee of Cladocai-pus distomus, 

 Clarke. SI 



This transverse slit-like opening advances a stage further by 

 the growth of its bordering walls, and by the consequent narrow- 

 ing of the middle portion of the slit. The approaching walls 

 -eventually meet, and the slit is divided into two distinct 

 apertures. Where such a process has occurred, the supracalycine 

 sarcotheca has three apertures, but occasionally one of the 

 terminal openings again seems to elongate and become divided, 

 so that four (three of them " terminal ") are sometimes present 

 (PI. Ixxxix., fig. 7, lower hydrotheca). Only one of the apertures 



s^ S. F. Clarke- Reports of the Sci. Res. Exped. to Eastern Tropical 

 Pacific by "Albatross," viii., The Hydroids — Mem. Mus. Comp. ZooL 

 Harvard, xxxv., No. 1, 1907, p. 17, pi. xiv., figs, 6, 7, and 10. 



