ZOOLOGY 



tinction between the endoplasm and ectoplasm found in these 

 and other Gymnomyxa is more apparent than real, and depends 

 only on the presence or absence of food and other granules, 

 the actual protoplasm of the organism being of one consistency. 



Some of the Lobosa have acquired the power of forming shells, 

 and this affords a convenient character by which we can divide 

 the class into two orders : (1) the N"uda, and (2) the Testacea. 



Order 1. Nuda. — The most famihar example of the 

 former order is the Amoeba, of which there are many species 

 quite distinct from the amoeboid spores of the Myxomycetes, 

 which are often taken for Amoebae. The various species differ 

 one from another in the nature of their pseudopodia and in the 

 character of their nuclei. In some species the former are little 

 more than low eminences, standing out from the general 

 surface, in others they are long finger-shaped processes which 

 stream rapidly hither and thither. Some members of this 

 order, as the Amoeba princeps and Pelomyxa, have numerous 

 nuclei scattered through the body : in the first-mentioned form 

 these arise by the gradual " fragmentation " of the original 

 nucleus. Such a multinucleated condition is constant in some 

 species. In some cases the soft protoplasmic body has been 

 observed to contract away from, and to lie within, a very thin 

 cuticular membrane, which maintains the outline that the 

 Amoeba possessed the moment before contracting ; this cuticle 

 is not usually visible, except in Zithamoeba, when it exists it 

 must be very attenuated and elastic. 



Pelomyxa is one of the largest of the Lobosa, the species P. 

 palustris having a diameter of more than 2 mm. The external 

 protoplasm is clear and produced into pseudopodia (Fig. 3). 

 The inner mass is crowded with vacuoles, and contains in addi- 

 tion to the numerous nuclei (5, Pig. 3) a number of refringent 

 bodies of unknown function (6, Fig. 3), and many food particles. 

 It has been observed to set free minute amoeboid spores, which 

 probably grow into new Pelomyxas. 



Order 2. Testacea. — The shell which encloses the proto- 

 plasmic body of these Lobosa may be soft and cuticular, and 

 may then be strengthened by grains of sand adhering to it, or 

 it may be hard. In either case the protoplasm can be extruded 

 from an aperture in the shell. Arcella (Fig. 4) is a common 



