370 



EVENINGS AT THE MICROSCOPE. 



from that already described. It is true I have detected 

 it only in Corynactis, where the short ectkoreum 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 ectkoreum in this kind of cnidce ; 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 

 question. 



Spiral Cnidse constitute the third 

 form.* In a few species, as Sagartia 

 parasitica, Tealia crassicor/iis, and 

 CeriantJms membranaceus, I have 

 found very elongated fusiform cnida 1 , 

 which seem composed of a slender 

 cylindrical thread, coiled into a very 

 close and regular spiral. In some 

 cases the extremities are obtuse, but 

 in others, as in T. crassicornis, an 

 example 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, such as one of the Cerithiadce or 

 Twrritelladae. The ecthoreum is discharged reluctantly 

 from this form, and I have never seen an example in which 



* Dr. Karl Mobiiss (Abhandl. Naturw. Yer. z. Hamburg, 1866), 

 considers this to be only an immature condition. — P. H. G., 1884. 



CNIDA OF CORYXACTIS. 



