276 GENERAL HISTORY OF THE IXFL'SORIA. 



going some important developmental change, the contents contract towards 

 the centre ; and then an external transparent and perfectly colomiess vesicle 

 becomes visible, while the flagellum and cilia disappear. The contracted 

 contents present a very definite and general spherical boundary, and are evi- 

 dently included in a distinct cell " — the primordial utricle. On a subsequent 

 examination of the pond in which the species examined occurred in prodi- 

 gious quantity, he found " immense masses " of the Peridinimn " towards 

 the bottom, where they appeared quite healthy, though presenting the condi- 

 tion described above as characterizing the quiescent state of the animalcule." 



Our imperfect information respecting the organization of the Peridinicea 

 renders any argimients concerning their nature unsatisfactory and inconclu- 

 sive. Perty, to whom we owe most of our knowledge respecting these crea- 

 tures, agrees mth Ehrenberg in assigning them an animal nature ; and we 

 gather from the few remarks Dr. Allman has made, that this opinion has also 

 the advantage of his support. Dujardin, we may add, treated the Peridinicea 

 as animalcules. Of the opposite opinion, viz. that they are members of the 

 vegetable kingdom, we know of no advocates, although some facts, such as 

 the apparent absence of the known internal stnictui'e of the Cihated Protozoa, 

 the non-contractility of their bodies, the character, colour, and changes of 

 their contents, might be adduced in its favour. However, the force of those 

 presumed facts will be much lessened by the consideration that the internal 

 organization of the Cihata may yet be discovered in these organisms when 

 they receive their due share of attention from microscopists, that even the ab- 

 sence of a mouth and rudimentaiy digestive tube would not absolutely exclude 

 them from the animal kingdom ; and that in the form and character of their 

 ciliary armature they present an animal much more than a vegetable type. 



Of their Vital Endowments, we may state that some swim mth consi- 

 derable activity by means of their flagellimi, aided, no doubt, by their ciliary 

 wreath, which probably gives the oscillating and rolling character to their 

 movements. 



They are inhabitants both of salt and of still fresh water, among aquatic 

 plants, but not of infusions ; and they disappear from water when long kept. 

 Most of the genus Peridinimn are marine. They may occur in such enormous 

 multitudes as to colour the pond or other collection of water in which they 

 have accumulated. Of this phenomenon Dr. Allman mentions an example 

 in which his Peridinimn uberrimum was so abundant in the ponds of Phoenix 

 Park, Dublin, as to colour' the water brown : — " 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 a hundred in extent." 

 This was in Jime ; in July " the coloration of the ponds had much increased 

 in intensity .... The colour in some parts was of so deep a bro^svn, that a white 

 disk half an inch in diameter became invisible when plunged to a depth of 

 3 to 6 inches, while a copious exit stream, which constantly flowed away 

 from one of the ponds, presented the same deep-brown tint." 



The most remarkable vital phenomenon presented by the Peridinicea, and 

 which is particularly common in them as a family, is that of phosphorescence, 

 which is possessed in a high degree by several of the marine species, having 

 a yellow or yellow-brown colour. In nine phosphorescent drops of sea- water 

 from near Kiel, taken up one after another by Ehrenberg, nothing save a 

 single individual of Pendinium (Ceratiu7n) Tripos was discoverable. Besides 

 this species, the following other Ceratia are phosphorescent, viz. Ceratiuni 

 Fusus, C. acuminatum, C. Michaelis, and C. Furca. 



Ehrenberg has reported the occiuTence of fossil Peridinicea ; but the or- 

 ganisms so considered are peculiar in having a silicious shell, which renders 



