601 FOURTH REPORT 1834. 



protrusion of the polypus is horizontal, or at right angles to 

 its surface. 



Cells are occasionally occupied by a large, irregularly round, 

 solid, yellow, ciliated animalculum, afterwards quitting them 

 to swim heavily below. Its motion relaxes, it becomes sta- 

 tionary, and dies, like the Plamilce, without speedy decompo- 

 sition. 



In just about the same spot also where the animalculum 

 became quiescent, a yellow nucleus is soon discovered, with a 

 pale diffusing margin. This enlarges as the nucleus declines ; 

 it gradually approximates the shuttle or slipper form of a cell, 

 and, converted to such, it gives birth in nine or eleven days to 

 a polypus. The adult Fhistra was vertical, but the new cell is 

 horizontal. One extremity, however, is already rising vertically, 

 which, extending after a similar fashion, proves the nidus of a 

 second polypus in nine or eleven days more. The protrusion 

 of the two animals now shows them at right angles to each 

 other. But as if the existence of the first were only a sole or 

 foundation for securing the superstructure in its growth, it 

 perishes as a third cell with its polypus forms above the second 

 by enlargement of the leaf. 



Thus there seems to be some relation between the spherules 

 occupying the cells and the originating Flustra ; but equal diffi- 

 culties require solution here as with the preceding race. 



5. Cristatella mirabilis. — Naturalists, attracted by the sin- 

 gular diversity of structure in the genus Serttilaria, and too 

 readily satisfied with mere external aspect, have devoted infi- 

 nitely more attention to the simple skeleton or tube than to 

 the animated parts. In as far as the author is aware, the tenta- 

 cula of all their polypi, together with those of the Flustra, 

 Tubularia, the Alcyonium, and Pennatula, are disposed in cir- 

 cular arrangement, the mouth being in the centre. Several 

 zoophytes of very diiFerent conformation inhabit the ponds, the 

 lakes, and the streams of Scotland ; among these the propa- 

 gation of the Cristatella mirabilis is chiefly considered by the 

 author, as the product itself seems to have eluded the research 

 of previous observers. 



Perfect specimens occur from six lines to twenty-four in 

 length, by two or three in breadth, of a flattened figure, fine 

 translucent green colour, and fleshy consistence. Some of the 

 shorter, tending to an elliptical form, may be compared to the 

 external section of an ellipsoid ; but those of the largest dimen- 

 sions are linear, that is, with parallel sides and curved extre- 

 mities. 

 • The middle of the upper and the whole of the under surface 



