liHIZOPODA. 25 



processes of sarcode, which can be thrust out at will, and which melt 

 again into the s\d:istance of the body when they are withdrawn. 



Tour jmncipal types of structure are known in the RIdzopoda, and 

 these constitute as many distinct orders, which are known by the 

 names of the Monera, Amiehsa, Foraminifera, and Hadiolaria. 



OiiDEK I. Monera. 



This name has been proposed for a small grouj) of organi.-m.^ 

 which are not only the lowest tyjies of the Ehizoijods, but may be 

 regarded as the most elementary foiriis of animal life known to 

 us. The Monera are minute protoplasmic organisms in which the 

 sarcode-body is neither defended by a thickened external envehjiie, 

 nor furnished with the structures known as the " nucleus " and 

 "contractile vesicle." Vacuoles and granules are |)resent in the 

 sarcode, and the pseudopodia emitted by the soft and mutable pro- 

 toplasm of the body are delicate and thread-like, or may be i-ainified 

 and variously interlaced (tig. 5). No hard covering or shell is ever 

 developed. The Jlonerj inhabit water, and are mostly marine. 



Okder II. Amiehea. 



This order is characterised by the fact t'liat tin' pxi:iuliipi)dl(i an 

 mostly hluiit and Jingerdike in shape, and that thu sarcixh: of tlte 

 body contains the structures known as the ^^ nvjdans^^ and ^'"contractile 

 vesicle." 



As the typ>e of the order may lie taken the Ainieaa or Proteus- 

 animalcule, so called because of the incessant anil varied changes of 

 form which it exhibits (Gr. amoihos, changing). The Amoeha is a 

 little microscopical creature which may conmionly be detected in 

 stagnant water, especially where there is decaying vegetable matter. 

 When examined under the microscope, all that wovUd probably be 

 seen at tirst would be a shapeless or irregularly sjiherical mass of 

 gelatinous, jelly-like sarcode, containing scattered granules. Soon 

 the creature might be observed to jjush out a iinger-sliaped ] ro- 

 longation of its own substance; and it would soon be found thr.t 

 similar jirocesses or pseudopodia could be ))uslied out at will from 

 almost any jjoint of the body and again retracted within it ■without 

 leaving any trace behind. As a result of this, the form of the 

 animal is constantly changing, and hence its common name of 

 Proteus-animalcule (tig. 3 and tig. 6 B). By means of these tem- 

 porary processes of sarcode, the Amaha both moves aiid obtains 

 food. Locomotion is effected in a. kind of creei>ing manner, the 

 animal pushing out the pseudopodia in one direction and then 



