288 EVENINGS AT THE MICROSCOPE. 



light that we have as yet upon either form is that of dim 

 conjecture. It has been supposed that, in both cases, the 

 function of the prehensile forceps is to seize minute animal- 

 cules or floating atoms of food, and pass them to the 

 mouth: but the supposition is involved in great diffi- 

 culties ; as the organs, however fitted for prehension, seem 

 peculiarly unsuited for transmitting objects ; besides that 

 the great majority of them are placed very remote from the 

 mouth. I can only repeat the conjecture which I hazarded 

 in the case of the Polyzoan " birds' heads," viz., that the 

 pedicellaria are intended to seize minute animals, and to 

 hold them till they die and decompose, as baits to attract 

 clouds of Infusoria, which, multiplying in the vicinity of 

 the Urchin, may afford it an abundant supply of food. 



There is yet another series of organs which stretch out 

 from every part of the surface of this living box ; scarcely 

 less numerous than either the spines or pedicellarice, but 

 very different from both. They are what I alluded to just 

 now as the feet. Let us pay a moment's attention to their 

 appearance and action, before we examine their structure. 



We see, then, extending from various points of the 

 shelly case of the Urchin, and reaching to twice or thrice 

 the length of the longest spines, slender pellucid tubes, 

 slightly tapering towards their free extremity, which then 

 abruptly dilates into a hemispherical knob, with a flat end. 

 These very delicate organs are extended or contracted at 

 the will of the animal, and turned in every direction, 

 waved hither and thither, and evidently have the faculty 

 of adhering very firmly by their dilated tips to any object 

 to which they are applied. 



So much we can discern as we watch the creature dis- 

 porting in this vessel of water ; but we will now endeavour 

 to learn a little more about its structure and economy. 

 Selecting for this purpose a sucker which is extended to 

 great length, I snip it across with a pair of sharp scissors, 

 as near the base as I can. Mark the result. The terminal 



