28 SYNOPTIC COLLECTION. 



ies" 1 that give rise to the Amoeba-like young (PI. 13, figs. 

 1-4). The little rods (PI. 13, fig. 10) are thought to be 

 parasitic plants. The streaming of the endosarc with its 

 vacuoles, rods, etc., into 'the hyaline ectosarc is well shown 

 in the drawing. 



If the flagellate condition is a normal stage in the devel- 

 opment of Pelomyxa and not a parasitic organism as main- 

 tained by some naturalists, the species is an exceedingly 

 interesting one. Observations on such forms as the whip- 

 bearing Rhizopods, Pelomyxa, and also those of Gruber 

 on Dimorpha mutans show that the amoeboid and flagel- 

 late conditions are marked in these less specialized organ- 

 isms by extreme variability, depending, it may be, upon 

 the need for slow or rapid motion. The flagellum arising 

 in this way as an adaptive character may become fixed in 

 the organization and finally inherited as a permanent 

 organ, which would seem to be the case in the Mastigo- 

 phora (= Flagellata). 



The group of Amoebina represented by DifHugia (PI. 

 14, fig. i) not only possesses many nuclei, but these have 

 become differentiated so that each contains one or more 

 nucleoli (fig. la). In addition to this specialization in 

 structure the protoplasm is not only capable of taking up 

 sand grains, like that of the Amoeba proteus, but it is able 

 to lay a part of these on the surface for a protective cover- 

 ing or shell. 



PI. 14, fig. i, is a vertical section through the shell and 

 body of Difflugia urceolata Carter. The hyaline ectosarc 

 extends out into the pseudopodia which are stretched from 

 the opening. In the protoplasm of the interior are seen 

 the nuclei colored red (PI. 14, fig. la, nucleus, uncolored 

 and magnified), besides sand and bits of nourishment. 

 Figs. 2-5 illustrate the division and shell formation of the 

 same species. In order to determine how the shell was 



*For views on this subject see Greef, Arch. f. mikr Anat., X, Sup- 

 plement; also Gruber, Zeitschr. f. wiss. Zool., XLI, 1885. 



