238 THE PROTOZOA 



the Rhizopoda by showing that the soft body was a plasmodium 

 containing numerous nuclei and chromidia, and forming a 

 pseudopodial network, but with no cell-differentiation or tissue- 

 formation. 



The body consists principally of a network of hollow tubes in 

 which the plasmodium is contained. The wall of the tubes con- 

 sists of, a hyaline organic substance resembling spongin. In the 

 interspaces between the tubes great numbers of foreign bodies 

 (" xenophya," HaeckeJ) are deposited, such as sand-grains, sponge- 

 spicules, Radiolarian skeletons, and so forth. In one family 

 (Stannomidce) the xenophya are held together by a system of threads, 

 ' linellae," in the form of smooth, refringent filaments, approxi- 

 mately cylindrical, which pass from one foreign body to another, and 

 are attached to them by trumpet-like expansions of their ends. 

 The substance of the linellae is doubly refractile and allied to spongin 

 in its chemical nature. Schulze compares them to the capillitium 

 of the Mycetozoa (see p. 241, infra). 



The protoplasmic body within the tubes contains, in addition 

 to nuclei and chromidia, enclosures of various kinds. Many tubes, 

 distinguished by the darker colour of their walls, contain quantities 

 of brown masses, apparently of faecal nature, and comparable to 

 the stercome of the Foraminifera (p. 233). In other tubes, lighter 

 in colour, there are found small, oval, strongly-refractile granules, 

 or " granellae," which consist chiefly of barium sulphate. Schulze 

 terms the system of stercome-containing tubes the " stercomarium," 

 and those that contain granellae the " granellasium." The tubes 

 of each system are distinguishable by their mode of branching, as 

 well as by their colour and contents. In the tubes of the granel- 

 larium the protoplasmic bodies are often found to contain isolated 

 cells or groups of cells, each with a single nucleus, which are prob- 

 ably stages in the formation of swarm-spores. Hence the sterco- 

 marium probably represents the purely vegetative part of the body, 

 in which the waste products of metabolism are deposited, while the 

 granellarium is a differentiated region of the plasmodium in which 

 the reproductive elements are produced. 



Nothing is known of the actual life-cycle of these organisms, but 

 from the appearances already described, seen in preserved speci- 

 mens, Schulze conjectures that they reproduce by formation of 

 swarm-spores, much as is known to take place in the Foram- 

 inifera. 



The affinities of the Xenophyophora .are seen to be with the 

 Foraminifera. In their habit of forming a skeleton of foreign 

 bodies they resemble the arenaceous Foraminifera, in which, how- 

 ever, the foreign bodies build up the house which directly encloses 

 the soft body, while in the Xenophyophora the soft body is en- 



