46 ZOOLOGY SECT. 



delicate ; in the number of nuclei ; and in the presence or absence 

 of a hard shell within or around the protoplasm. The following 

 five orders may be distinguished : 



ORDER 1. LOBOSA. 

 Rhizopoda with short, blunt pseudopods. 



ORDER 2. LABYRINTHULIDEA. 



Rhizopoda having a network of fine pseudopods, in which 

 corpuscles travel to and fro. 



ORDER 3. FORAMINIFERA. 



Shelled Rhizopoda with fine, branched, and anastomosing 

 pseudopods. 



ORDER 4. HELIOZOA. 



Rhizopoda with fine, stiff, radiating pseudopods. 



ORDER 5. RADIOLARIA. 



Rhizopoda having a shell in the form of a perforated central 

 capsule, and usually, in addition, a siliceous skeleton : the pseudo- 

 pods are long and delicate. 



Systematic Position of the Example. . 



Amoeba proteus is one of many species of the genus Amceba, 

 belonging to the family Amcebidce, of the order Lobosa. The blunt 

 pseudopods not uniting to form networks place it among the 

 Lobosa : the absence of a shell among the Amoebida?. The genus 

 Amoeba is distinguished by the presence of one or more nuclei, 

 and of a contractile vacuole. In A. proteus the pseudopods are 

 of considerable length and sometimes branched, and there is a 

 single nucleus, having its chromatin in the form of scattered 

 granules. 



* 



ORDER 1. LOBOSA. 



General Structure. The members of this group all agree 

 with Amoeba in essential respects, their most characteristic feature 

 being the short, blunt pseudopods. The chief variations in struc- 

 ture upon which the genera and species are founded have to do 

 with the number and character of the nuclei, the form of the 

 pseudopods, and the presence or absence of a shell. 



In Amoeba itself there may be one (Fig. 27, E) or several (B) 

 nuclei, the chromatin of the nucleus may be arranged in various 

 ways (F, H), and the pseudopods may be prolongations of con- 



