286 EVENINGS AT THE MICROSCOPE. 



of most exquisite beauty. The material has all the trans- 

 parency and sparkling brilliance of flint-glass, while the 

 elegantly-shaped pins, the perfect symmetry of the bases, 

 the arch which is lightly thrown across their cavity, the 

 minute teeth of the tips locking accurately into each other, 

 and the oval cavities in the whole structure set in regular 

 rows, and reflecting the light from thousands of points, 

 constitute a spectacle which cannot fail to elicit your 

 admiration. 



P. globifera is formed on the same model as P. triphylla, 

 but is more globose, and each piece appears to have a 

 deep cleft at the point, which does not extend to the inte- 

 rior side, where a thick ridge runs down from the point to 

 the base. At the summit of this ridge, in each of the three 

 divisions, there is set a strong acute spine, directly hori- 

 zontally inwards, so that the three cross each other when 

 the blades close, which they do energetically, — a formida- 

 ble apparatus of prehension I The stem is much more 

 slender than in P- triphylla, and the height of the head of 

 one of average size is only -i^ii of an inch. It is peculiar 

 also in being slender throughout, and in having the knobbed 

 calcareous stalk extending up to the head, which appears 

 to work on it. In each of the other sorts the stalk extends 

 only through a part of the distance, above which the in- 

 vesting fleshy neck becomes wider and empty. 



But the internal structure is not quite the same as in 

 the others. The main portion of the head is composed of 

 gelatinous flesh ; the calcareous support being reduced to 

 that ridge which runs up the interior side of the blade. 

 This is somewhat bottle-shaped, with a bulbous base, and a 

 long slender neck, with two edges on the inner face, which 

 are armed with horizontal hooked spines, some of which are 

 double ; and the whole terminates in a sort of ring, formed 

 by the last pair of spines, which unite into the acute hori- 

 zontal point that I have already mentioned. The skeleton 

 is filled with oval cavities, like that of the others. 



