PKOTOZOA : FORAMINIFERA. 47 



podia there is a constant circulation of granules in different 

 directions. This singular phenomenon is in many respects 

 analogous to the circulation of granules which is seen in 

 many vegetable cells, and it is believed by Dr. Carpenter that 

 * the conditions of the two sets of phenomena are essentially 

 the same.' 



The shells of Foraminifera may be classed in three divisions, 

 termed respectively the * porcellanous,' the ' hyaline ' or 

 'vitreous,' and the 'arenaceous.' The porcellanous shell is 

 quite homogeneous in its composition, is opaque- white when 

 seen by reflected light, and is not perforated by pseudopodial 

 foramina. In these forms (e.g. Miliola) the pseudopodia are 

 emitted solely from the mouth of the last-formed segment of 

 the shell. The vitreous shell is transparent and glassy in 

 texture, and its walls are perforated by numerous pseudopodial 

 apertures. The arenaceous shell is properly speaking not a 

 true ' test,' since it is simply composed of particles of sand 

 united together by some unknown cement. Its walls may or 

 may not be traversed by pseudopodial foramina. 



As regards the form of the shell, the Foraminifera may be 

 conveniently, though arbitrarily, divided into two sections : 

 the Monothalamia and the Polythalamia. In the first of these 

 sections (fig. 4), comprising the so-called 'simple 'or 'uni- 

 locular' Foraminifera, the shell consists of a single chamber, 

 and the animal is, in fact, nothing more than a little mass of 

 sarcode enveloped in a calcareous covering. Lagena, with its 

 beautiful flask-shaped shell, may be taken as the type of this 

 division. In the Polythalamia, or ' multilocular ' Foraminifera, 



Fig. 4. Monothalamous Foraminifera. a. Lagena sulcata. b. Adult form of the 

 same. c. Lagena inalo. 



the shell is composed of many chambers separated from one 

 another by divisional walls or ' septa' (fig. 5), each of which is 

 perforated by one or more openings, 'septal apertures,' by 

 means of which the sarcode occupying the different chambers 

 is united into a continuous and organic whole, the connecting 

 bands being called ' stolons.' Complex as their structure 

 often is, the compound Foraminifera are, nevertheless, formed 

 by a process of continuous gemmation or budding from a 

 single 'primordial segment' in every respect identical with 



