FORAMINIFERA. 537 



gradually replaced in the newer strata, by species more allied to 

 those at present existing in temperate climates. This is one of the 

 many facts, which tend to prove that this part of the earth had, 

 at some former period, a much higher temperature than at present. 

 1110. Under the class Polypifera, we are probably to include 

 a large and very important group of minute calcareous structures, 

 which, from their strong resemblance to the spiral-chambered 

 shells of some Cephalopoda ( 894), have been supposed to be 

 formed by animals of that class. Many kinds of them exist on 

 almost every sandy shore ; but their extreme minuteness causes 

 them to be usually overlooked, and is also an obstacle to the 

 satisfactory determination of the character of the animals which 

 construct them. By D'Orbigny, who first attracted the atten- 

 tion of Naturalists to the details of this curious group, it was 

 regarded as an order of Cephalopoda; and he gave to it the 

 name of Foraminifera, on account of the communication 

 between the chambers not being established by one principal 

 tubular aperture, the siphuncle, but by numerous minute 

 foramina or porous orifices. The species which exist on the 

 shores of Northern Europe are so minute, as not to be easily 

 examined, even with the microscope ; but those which are found 

 in the Adriatic Sea, are sufficiently large to be recognised with the 

 naked eye. From an examination of recent specimens, it has 

 been ascertained that the animals by which these shells are con- 

 structed resemble polypes more than any other group, although 

 allied also to the Polygastric Animalcules ; and that we are 

 thus to regard these little isolated masses as coralline structures, 

 each being formed by the continual growth of one individual. 

 The character of the animal appears very simple. No part of it 

 is seen externally, except when it is preparing to add a new 

 chamber to its shell. It seems to consist of a series of mem- 

 branous bags, united together like a string of beads, in the outer 

 layer of which is deposited the calcareous matter that gives the 

 shell-like character. If this latter be removed by a weak acid, 

 the animal membrane will be left ; and the spiral may then be 

 unrolled. Whether any of the species possess a regular mouth 

 and tentacula, is yet uncertain. 



