36 COMPOUND ORBITOLITE. PART in. 



very different, but the sarcode segments in all the three 

 are so connected as to form a very complex compound 

 animal. 8 Different as this structure is from that of 

 the simple Orbitolite, they are merely varieties of the 

 same species ; for it has been shown by Dr. Carpenter 

 that, although many pass their lives in the simple one- 

 storied state, they may change into the complex form 

 at any stage of their growth ; and as an equally exten- 

 sive range of variation has been proved by Professor 

 Williamson and Mr. Parker to prevail in other groups 

 of Foraminifera, the tendency to specific variation 

 seems to be characteristic of that type of animal life, 

 and consequently the number of distinct species is less 

 than they were supposed to be. 



The Orbitolites are found in the dredgings of all the 

 warmer seas, in vast multitudes at the Philippine Islands, 

 but those from Australia are the most gigantic, being 

 sometimes the size and thickness of a shilling. 



Order of Arenaceous Foraminifera. 



In the numerous family of Lituolidse the abode of the 

 animal consists of a cement mixed with very fine par- 

 ticles of sand with larger ones imbedded in the surface. 

 The order includes a wide range of forms divided into 

 three genera, the simplest of which consists of a cylin- 

 drical tube twisted into a spiral gradually increasing 

 in diameter, and attached to a foreign substance by one 

 of its surfaces. The creature which lives in it is a 

 uniform cord of sarcode, which sends its pseudopodia 

 out through a large aperture at the extremity of its 

 tube in search of food. Although the tube consists of 

 sand imbedded in an ochreous-coloured cement secreted 

 by the animal, its surface is smooth as a plastered wall. 



8 A complete description of this complex type is given by Dr. Carpenter 

 in the Phil. Trans. 1856. 



