104 FRESHWATER RHIZOPODS OF NORTH AMERICA. 



of the structuie of the sarcode of Difflugia piriformis, indicates two dif- 

 ferent conditions or stages as above described. The chlorophyl granules, 

 when present, he regards as part of the structure of the animal, as much so 

 as the same colored element is, in the green fresh-water polyp (Hydra 

 viridis). Colorless granules, in association with the green ones, he deter- 

 mined to be of the nature of starch, and these he also regards as part of 

 the structure of the animal. In the colorless stage of the latter he further 

 intimates the absence of the chlorophyl and a diminution in the quantity 

 of the starch.* 



According to the same able investigator, the green condition of the 

 sarcode is associated with greater activity of the animal, and is especially 

 common in the spring season; while the colorless condition, indicative of 

 more passive habit, occurs in autumn. The changes in color he supposes 

 to be connected with changes in the nucleus, and to be related with the 

 reproductive process. 



The Swarthmore specimens, above mentioned, found in such profusion 

 in the summer of 1874, were all possessed of a bright green endosarc, and 

 were in the most active condition. Neither before nor since have I met 

 with any form of Difflugia which exhibited more lively movements, and 

 such varied changes in the appearance of the pseudopods Extreme 

 extension of the latter was accompanied by an influx of more or less of the 

 endosarc with chlorophyl and starch-like granules. Of the many changes 

 presented by the pseudopods, examples are given in the figures of pi. XI. 



While it has occurred to me to see multitudes of Difflugia pyriformis in 

 all its varieties of the ordinary form, and of D. compressa, D. nodosa, and D. 

 vas, with the sarcode in a bright green condition, at all temperate seasons 

 of the year, I have also observed them in the colorless condition in variable, 

 but comparatively small, proportion, at the same times and in the same 

 localities. The animal is also to be seen of every grade, from that in which 

 the body of the shell appears in greater part to be occupied by a bright 

 green endosarc, to that in which all color is absent except what is due to 

 the presence of food. Commonly, when the bright green specimens of D. 

 pyriformis are abundant, the uncolored ones are comparatively few. I have 

 further observed bright green specimens of D. pyriformis, in which the sar- 

 code was not only in a passive condition, but was contracted into a central 



* Annals and Magazine of Natural History, xii, 18fi:i, 249. 



