AMCEBA PROTEUS. 47 



separated, and their posterior position may be tem- 

 porarily lost. According to Penard the elliptic, discoid, 

 punctated nucleus is characteristic of this species. 



In the larger examples of Amoeba proteus the pos- 

 terior ectoplasm habitually contracts, and, in doing so, 

 forms a mass of " short digitate or mulberry-like 

 processes." These, however, are not permanent. They 

 appear to be modified or latent pseudopodia, which 

 are, so to speak, grouped together and dragged behind 

 by the animal in its progress. In some, and those 

 always the largest individuals, they are conspicuous. 

 Leidy's observations showed that they eventually get 

 absorbed in the general mass, or, in response to some 

 change in the creature's motion, develop into active 

 pseudopodia and are used as such. 



The endoplasm of A. proteus is usually charged with 

 a considerable variety of extraneous material. Inter- 

 mixed with chlorophyl-pellets there may be seen re- 

 fringent bodies resembling oil-globules, and granules 

 of starch. The former are probably adventitious sub- 

 stances, of no significance physiologically, though 

 Leidy was of opinion that they might prove to be an 

 intrinsic element. The starch-grains may have been 

 incepted with the food. There are, in addition to 

 these, minute crystals of quartz or calcium carbonate, 

 or both, in variable quantity. 



Although the food of A. proteus consists for the most 

 part of chlorophyl-bearing algae, such as diatoms and 

 desmids, the animal, like others of its class, preys occa- 

 sionally on other Protozoa, and even on the Rotifera. 



Plate I, fig. 3, and PI. Ill, f. 2, represent a remark- 

 able variety, distinguished by its mulberry- shaped 

 caudal extremity and finely-granular endoplasm. In 

 the latter there is no admixture of oil-like globules or 

 other adventitious matter, but green corpuscles are 

 present, which in all the examples met with were of 

 uniform size and very numerous. The nucleus and 

 contractile vesicle are normally as in A. proteus, but in 

 general aspect and mobility this form is so distinct as 



