RHIZOPODA. 



We may then divide the whole of the Rhizopoda into four orders : I. Lobosa ; 

 II. Eadiolaria ; III. Heliozoa ; IV. Reticularia. 



Order I.— LOBOSA. 



The Lobosa are characterized by Ijlunt, digitate extensions {pseiulopodia) of the 

 soft body-mass, by means of which the animals move about and capture their food. 

 The animals may be unprotected by a covering of any kind, or they may have shells of 

 chitinous material or of cemented grains of sand or debris of any kind. The soft body 

 is similar in structure in all cases, and the naked form known as the Amoeba affords 

 the best subject for studying this group of animals. 



The Amoeba x>roteus is represented in Fig. 2, and may be taken as a type of all 

 the lobose protoplasts. It consists of an outer portion of protoplasm, termed the 

 ectosarc, rather more consistent and clearer than the rest, but continuous with it, and 

 an inner, more fluid portion, containing granules and known as the endosarc. There is 

 no permanent differentiation between the endosarc and the ectosarc, for as the animal 

 moves, or takes in particles 

 of food, portions of the 

 ectosarc may become in- 

 folded, and they then im- 

 mediately become conflu- 

 ent with the endosarc. 

 Probably the only differ- 

 ence between the two 

 portions of the proto- 

 plasm is that caused by 

 contact with the surround- 

 ing water, which seems to 

 ]:)artially coagulate the ex- 

 ternal portion. The Am- 

 oeba moves by extending a 

 portion of the clear ecto- 

 sarc in any direction, when 

 the granules of the endosarc will be seen to follow, as though flowing into an empty space. 

 The form of the Amceba is therefore constantly changing, — pseudopodia are projected 

 in any direction, singly or several at one time, while the granules are in constant 

 motion. 



The granules do not seem to be essential constituents of the protoplasm. They are 

 of all sizes, from almost immeasurably minute particles up to comparatively large ones. 

 They seem to be inert particles, many of them doubtless being the remains of sub- 

 stances collected as food, but frequently there are seen globules of oil and spherical 

 gi'een corpuscles which are supposed to contain chlorophyl. 



Within the endosarc a nucleus is often readily observed. A nucleus is regarded as 

 an essential element in the Rhizopod structure. It appears as a spherical oi- discoid, 

 colorless, clear, or granular corpuscle, within which may or may not be seen a still 

 smaller body known as the nucleolus. 



- AiiKEba proteuSj greatly enlarged. 



