24 DK. ALLMAN ON 



paper in the shade are of a dull yellowish-green ; but if these 

 be now exposed to the direct rays of the sun, for about ten 

 minutes, they will be found to have assumed a bright bluish- 

 green, which they do not again lose. 



During decomposition in water a fluid is produced, which 

 is of a claret-red under reflected light, but of a fine grass-green 

 when viewed by transmitted light. 



Tlie next subject to which 1 would draw attention is a 

 species of Peridinea, which had just shown itself in such 

 inconceivable multitudes as to give rise to a peculiar colora- 

 tion of some of the ponds in the Phoenix Park. During the 

 last three weeks a spectator on the banks of the large ponds * 

 m the Park must have been struck by a brown colour assumed 

 by the water. This colour was sometimes uniformly diffused 

 through the water ; at other times it appeared as dense clouds, 

 varying from a few square yards to upwards of 100 in extent. 



A microscopic examination of the water proved the brown 

 colour to be entirely due to the presence of a minute organism, 

 which, though it does not exactly agree with any published 

 generic description, 1 have tliought it better, by slightly 

 modifying tlie genus Peridinea, as characterised by Ehrenberg, 

 to place it in that genus rather than construct for it a new 

 one. 



It varies from the 1-lOOOth to the l-500th of an inch in 

 diameter, and approaches in form to a sphere (Plate III., 

 figs. 9, 10), divided by a deep annular furrow into two hemi- 

 spheres, on one of which is situated another furrow, springing 

 vertically from the annular furrow, and terminating at the 

 pole. The organism under consideration may be regarded as 

 essentially a solitary cell ; it encloses reddish-brown granular 

 contents, and a large, well-defined central nucleus. In the 

 midst of the contents are numerous clear spaces, of various 

 sizes, which, however, appear to be oil-drops rather than true 

 vacuolae. 



In most instances a deeper-coloured ocelliform spot was 

 evident near the polar extremity of the vertical furrow. 



It is eminently locomotive, swimming with great activity 

 by the aid of a flagelliform appendage, which springs from the 

 vertical furrow near the point of junction with the other, and 

 of very minute vibratile cilia, which seem distributed over the 

 surface, and not confined to the furrows, as maintained by 

 Ehrenberg, in the species of Peridinece described by him. 



Before death, and also when only passing from a motile to 



* The two large ponds communicate with one another, and together 

 occupy a space of about 14 acics. The observations were made in June, 

 1854. 



