842 



EVENINGS AT THE MICROSCOPE. 



The structure of these tentacles is very interesting. 



The stem contains a core 

 or central chain of large 

 cells, which take a some- 

 *what square outline from 

 mutual pressure. The sur- 

 face is roughened with 

 small swellings, from each 

 of which projects a long 

 and extremely attenuated 

 hair (palpocil), which is 

 probably a very delicate 

 organ of touch. The ter- 

 minal globe is filled with 

 proportionately large oval 

 vesicles, each with a cen- 

 tral cavity, which are 

 arranged in a divergent 

 manner around the centre, 

 so that their tips shall 

 reach the surface of the globe ; these are those potent 

 weapons of offence called thread-cells (cnida). The sur- 

 face of the globe is covered with short thick palpocils, 

 which Dr. T. S. Wright considers as prehensile organs. 

 " These palpocils arise, each as a somewhat rigid process, 

 from the side of one of the large thread-cells, buried in the 

 head of the tentacle ; and they probably convey an im- 

 pression, from bodies coming into contact with them, to 

 the thread-cell, causing the extrusion of its duct.'' 



Besides these globe-headed tentacles, there are, on the 

 lower part of the club-foot, four other organs similar in 

 every respect, except that they are not furnished with 

 heads, nor any terminal dilatation whatever. They pro- 

 ject horizontally as the knobbed ones, but their origin, 

 and the respective lines of their radiation, are intermediate 

 or alternate ; in other words, if we consider the globe- 



STAUR1DIA. 



