528 MANUAL OF NATURAL HISTORY. 



tended, but abound more in tropical, shady- 

 woods. 



5. Family. — Liver-worts (Marchantiaceae). Stem or 



axis leafless, but bordered by membranous 

 expansions which sometimes unite at their 

 margins, forming a broad lobed frond ; spore- 

 cases in heads, stalked, opening by irregular 

 fissures, or by separate teeth ; spores globose. 

 Inhabit damp, shady places, everywhere. 



6. Family. — Crystal-worts (Ricciacese). Submerged 



or floating plants, usually annual ; leaves and 

 stems blended into a cellular frond ; spore- 

 cases membranous, decaying so as to permit 

 the spores to escape; elaters none. Most 

 abundant in Europe, but occur also in most 

 parts of the world. 



THALLOGENS. 



With Thallogens we reach the extremes of another 

 primary division of nature, those confines where 

 the vegetable and animal forms of vitality appear to 

 encroach upon each other, where cell-life in its most 

 simple and primitive form puzzles alike the Phyto- 

 logist and the Zoologist. In the great anxiety which 

 has been evinced to come to a determination on 

 this point, it has been alleged that there is an inter- 

 mediate stage, by which the one kingdom passes 

 into the other, and some have fancied that they 



