. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. 370 EVENINGS AT THE MICROSCOPE. from that already described. It is true I have detected it only in Corynactis, where the short ecthoreum of the Tangled Cnida is surrounded throughout its length by a barbed strebla of three bands. The barbs are visible, under very favourable conditions for observation, even while the tangled wire remains inclosed in the cnida, but their optical expression is that of serratures of the walls, without the least appearance of a screw.
. Evenings at the microscope : or, Researches among the minuter organs and forms of animal life . Zoology; Microscopy; Microscopes. 370 EVENINGS AT THE MICROSCOPE. from that already described. It is true I have detected it only in Corynactis, where the short ecthoreum of the Tangled Cnida is surrounded throughout its length by a barbed strebla of three bands. The barbs are visible, under very favourable conditions for observation, even while the tangled wire remains inclosed in the cnida, but their optical expression is that of serratures of the walls, without the least appearance of a screw. This, I say, is the only species in which I have actually seen the arma- ture of the ecthoreum in this kind of cnida, but I infer its existence from analogy in other species, where the conditions that can be recognised agree with those in this, though the excessive attenu- ation of the parts precludes actual observation of the structure in ques- tion. Spiral Cnidse constitute the third form. In a few species, as Sagartia parasitica, Tealia crassicornis, and Ce- rianthus membranaceus, I have found very elongated fusiform cnida, which seem composed of a slender cylin- drical thread, coiled into a very close and regular spiral. In some cases the extremities are obtuse, but in others, as in T. crassicornis, an ex- ample of which I now show you, the posterior extremity runs off to a finely-attenuated point, the whole of the spire visible even to the last, the whole bearing no small resemblance to a multispiral shell; as one of the Cerithiada or Turritellada. The ecthoreum is discharged reluctantly from this form, and I have never seen an example in which the whole had been run off. So exceedingly subtle are the walls of the cnida, that it was not until after many observations that. CNIDA OF Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not
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