PROTOZOA. C91 



the Polygastrica have a single stigma ; some, as the Distigma, 

 have two. They never sleep, and are most tenacious of life. 

 The reproduction occurs by spontaneous division and by gem- 

 mation or budding. The division goes on with wonderful rapid- 

 ity, either transversely or lengthwise, each half forming an 

 independent animal. Ehrenberg asserts that the Hydatina seta, 

 increased in twelve days to sixteen millions, and another species 

 in four days to one hundred and seventy billions. 



The Infusoria are generally colorless and translucent; but 

 some are green, some yellow, and a few red. The colored spe- 

 cies give their peculiar tinge to the water. The shape is globu- 

 lar, oval, spindle- like, cylindrical, or vermiform. Some are 

 continually changing their form, as those of the genus Amceba 

 or Proteus, belonging to the ANENTERA. This -'consists of a 

 mass of clear jelly-like matter, with a few granules, two or three 

 supposed stomachs, and a contractile bladder," and from its 

 power of changing its form, has u long been celebrated among 

 naturalists." 



The term FORAMINIFERA, or RHIZOPODS, is restricted to ani- 

 mals of low organization, ' consisting of a slimy, transparent 

 jelly, invested with a hard,usually calcareous shell." They 

 are found in sea-sand, and amongst marine refuse dredged up 

 from deep water. Owing tp the spiral form of many of their 

 shells, these creatures were long erroneously regarded as mol- 

 lusks, and as allied to the Nautilus. Ehrenberg thought them to 

 be allied to the Bryozoa or Moss-corals, (minute animals aggre- 

 gated in great numbers like the coralligenous Zoophytes, having 

 a distinct stomach, and an intestine curved upon itself, with an 

 outlet near the mouth, " the tentacles of which are covered with 

 vibrillse, and covered with a membranous, horny, or calcareous 

 tube ; now referred to the Tunicates or lowest class of Mollusks.") 

 But the true position of the Foraminifera is probably between the 

 Ameeba on the one hand, and. the sponges on the other. The 

 Foraminifera in the calcareous shell, present various appear- 

 ances. Sometimes they are comparatively large and conspicu- 

 ous ; at others so small that their existence can be shown only 

 by means of high magnifying powers. Through the foramina, 

 long delicate processes of the soft animal, termed pseudopodia, 

 (or false feet-like,) are protruded. These are probably used to 

 some extent, " for tactile, prehensile, and locomotive purposes, or 

 for the imbibition of nutritive fluid." 



The Foraminifera have peculiar interest for the geologist. 

 Recent strata owe their origin to the long continued accumula- 

 tion of these minute atoms. White chalk rocks are mainly com- 



