378 APPENDIX. 



without a permanent mouth or stomaoh. It has the power of extending 

 out portions of its protoplasmic "body in the form of thread-like processes, 

 and thence the name Rhizopod, signifying root-like feet. Many of the 

 species secrete shells, and although the shell of a single animal may not 

 be larger than the point of an ordinary pin, it has pores or foramina 

 through it which give exit to the thread-like processes ; and the shells 

 are therefore called foraminifers. 



Rhizopods occur often as solitary animals ; but generally, like polyps, 

 they multiply by budding, and thus make groups of cells, some of the 

 larger of which have the magnitude of a quarter of a head of a pin ; of 

 this nature are the Globigerinse, and various other kinds, common over 

 the bottom of the deep ocean, as well as in many shallow waters. A few 

 form, through the budding process, disk-like or coin-shaped foraminifers, 

 half an inch to an inch in diameter ; and such are the Orbitolites, re- 

 ferred to, on page 152, as contributing largely to the coral reefs of the 

 Australian seas, while common throughout the reef regions of the Pa- 

 cific. 



In one division of Rhizopods — that including the Globigerinse and 

 Orbitolites — the foraminifers are calcareous ; in another, they consist of 

 agglutinated sand ; in another (that of the Polycystines) they are sili- 

 ceous. 



In another section of Protozoans called the Flagellate Infusoria, and 

 including the Monad, there is a permanent mouth, and often a slender 

 process (flagellum) which appears to serve the mouth by pushing in 

 food. The animals are much more minute than the Rhizopods. In this 

 section, as Prof. II. James Clark has shown, belong the sponges — a 

 sponge being a compound group of these living infinitesimals, produced 

 by growth and budding. 



A third division of Protozoans is that of the Vorticellse and related 

 forms. They have at top a circle or spiral of cilia, around a disk, in one 

 part of which disk the mouth is situated. These beautiful species — occa- 

 sionally large enough to be visible -to the naked eye — often grow in clusters 

 resembling somewhat those of the Hydroids and Bryozoans. 



