PROTOZOA I FORAMINIFERA. 6 I 



seen by reflected light, and is not perforated by pseudopodial 

 foramina. In these forms (e.g., Miliola, fig. 4, b) the pseudo- 

 podia 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 shell secreted by the animal, 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. 7, a), 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 

 carcode enveloped in a calcareous covering. Lagena (fig. 8, A) 



A B c 



Fig. 8. Diagram to illustrate the formation of the compound Foraminffera. A, 

 Simple form (Lagena), consisting of a sphere of sarcode, surrounded by a cal- 

 careous shell ; B, Compound form, produced by linear gemmation from a primitive 

 segment resembling A (Nodosarid) ; C, Compound form (Discorbina], in which the 

 buds are thrown out in a spiral, the coils of which lie in one plane. 



with its beautiful flask-shaped shell, may be taken as the type 

 of this division. Another well-known unilocular form is 

 Entosolenia, which is like Lagena in shape, but has the tubular 

 neck reversed, so as to be inserted into the interior of the test. 

 In the Polythalamia, or " multilocular " Foraminifera, the shell 

 is composed of many chambers separated from one another by 

 divisional walls or "septa" (fig 7, c, d, e\ each of which is per- 

 forated 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 



