It is supposed that during the growth of the Orbitolite, when the animal becomes too large for its abode, its pseudopodia coalesce and form a gelatinous massive coat over the margin of the exterior zone, which secretes a shelly ring with all its chambers and passages, each ring being a mere vegetative repetition of those preceding it. That vegetative property enables the animal to repair its shell or add a part that is wanting. For, if a small portion of a ring be broken off and separated from the living animal, it will increase so as to form a new disk, the want of the central part or nucleus not appearing to be of the smallest consequence; indeed, the central rings are very often imperfect. The sarcode of these animals is red, and although the shell is of a brownish-yellow by transmitted light, it is so translucent that the red tint is seen through it. The simple Orbitolite has many varieties. Sometimes it begins its life as a spiral which changes to a circular disk as it advances in age. It varies in thickness, and some of its very large varieties may be said to consist of three disks or stories of concentric chambers and many marginal pores instead of one. The upper and base stories of concentric chambers are alike, the intermediate one 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 extensive 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._