THE LOBOSA 



81 



of long digitate pseudopodia ; several nuclei ; no contractile vacuoles. 

 Zooxanthellae occur in the protoplasm. Marina 



Pelomyxa, Greeff. A remarkable genus of Gymnamoebida found in 

 the mud of ponds and ditches, and distinguished by the presence of an 

 enormous number of minute nuclei. Several species have been described. 

 P. palustris, Greeff, P. villosa, Leidy, 

 are frequently found in this country 

 and are probably cosmopolitan. P. 

 penardi, Rhumbler (22), was found 

 at Gottingen. P. viridis has only 

 been found in British India. 



They vary considerably in size, 

 but when spread out in progression 

 P. viridis may attain to a size of 8 

 mm. in diameter, and the other 

 species to 2 mm. 



The form of the animal is like 

 that of an amoeba, and progress is 

 effected by means of numerous 

 blunt lobose, villiform, or some- 

 times attenuate and anastomosing 

 pseudopodia of very variable form 

 and length. There is neither test FIG. 14. 



nor enveloping membrane. Pelomyxa palustris, Greeff. An example 



T , . with comparatively few food particles. (After 



In the ordinary vegetative con- Qreeff.) 



dition of Pelomyxa there are very 



many nuclei. Bourne (3) calculated that in a large specimen of P. viridis 

 there may be 10,000 nuclei. In addition to the nuclei there are numerous 

 minute scattered chromidia (Bott [2]) (Fig. 7). These chromidia may be 

 clearly seen in the ectoplasm. The chromidia are formed by the chromatin 

 discharged from the nuclei, and they never unite to form a chromidial 

 network. In addition to the nuclei and chromidia, the cytoplasm contains 

 refringent bodies of a proteid nature (Veley [34]), numerous symbiotic 

 bacteria, food - vacuoles, and various water - vacuoles, and minute 

 vesicles. 



The refringent bodies appear to be waste materials and probably a 

 by-product of metabolism, and are undoubtedly used as the food material 

 of the symbiotic bacteria. They are sometimes ejected from the body, 

 but in general the Pelomyxa relies on the bacteria as scavengers to 

 clear its protoplasm of these bodies. The life-history of the symbiotic 

 bacteria (Oladothrix pelomyxae) has been studied by Veley, who also 

 determined the proteid nature of the refringent bodies by obtaining the 

 characteristic reactions with (1) Millon's reagent ; (2) sugar and sul- 

 phuric acid ; (3) the xanthoproteic test ; and (4) with caustic soda and 

 copper sulphate. 



The green vesicles described by Bourne in P. viridis appear to be of 

 the same nature as the refringent bodies, but stained with chlorophyll 



The protoplasm of all the species contains a number of vacuoles and 

 vesicles, but none of them appear to be rhythmically contractile. 



