68 MANUAL OF ZOOLOGY. 



spines, in consequence of this structure, are able to serve for the 

 transmission of the pseud opodia, which gain the exterior by 

 running through the canals and escaping at their apices. Many 

 of the pseudopodia, however, do not occupy the canals of the 

 spines. 



II. FAM. POLYCYSTINA. The members of this family are 

 closely related to the Foraminifera, differing from them chiefly 

 in the fact that their shells are composed of flint instead of 

 carbonate of lime, as in most of the latter. They possess a 

 body of sarcode, which is enclosed in a foraminated siliceous 

 shell, which is often furnished with spine-like processes, and is 

 usually of great beauty (fig. 10, b). The sarcodic substance of 

 the body is olive-brown in colour, with yellow globules, and 

 often does not entirely fill the shell. The pseudopodia are 

 emitted through the foramina in the test, and are long, ray-like 

 filaments, which display a slow movement of granules along 

 their borders. 



The Polycystina are all microscopic, and are all inhabitants 

 of the sea, having a very wide distribution. They are also 

 found abundantly in certain Tertiary deposits, being often erro- 

 neously described as Diatomacea. 



III. FAM. THALASSICOLLIDA. The 'Thalassicollida have been 

 defined as being Rhizopoda which are " provided with structureless 

 cysts containing cellular elements and barcode, and surrounded 

 by a layer of sarcode, giving off pseudopodia, which commonly 

 stand out like rays, but may and do run into one another, and so 



form networks' 1 ' 1 (Huxley). 



The Thalassicollida may be simple or composite, the latter 

 consisting essentially of aggregations of the former; whilst 

 these are fundamentally composed of a mass of granular proto- 

 plasm, containing a nucleus, but without a contractile vesicle, 

 " enclosed in a membranous capsule, which is in turn protected 

 by a more or less thick gelatinous exudation, whilst numerous 

 sarcoblasts occur scattered through the endosarc, and occa- 

 sionally a few may be seen suspended within the external gela- 

 tinous stratum " (Wallich). The whole organism is supported 

 by more or less extensively developed skeletal structures. The 

 skeleton may be simple, consisting of a delicate fenestrated 

 shell ; or may be compound, consisting of a number of spicular 

 masses. 



The three best-known genera of the family are Spharozoum, 

 Collosphcera, and Thalassicolla. They are all marine, being 

 found floating passively at the surface of most seas ; and they 

 vary in size from an inch in diameter downwards. Sphcerozoum 

 consists essentially of a number of spherical sarcode-bodies 



