14 PROCEEDINGS OF THE ACADEiMY OF 



Of the genus Arcdla^ A. vulgaris and A. dentata, with their 

 varieties, are common with us. In the genus Difflugia the lilce- 

 ness of our species to those of Europe is strilcing. Besides D. 

 2)roteiformis, D. acuminata^ D. comjji-essa, D. pyriforini.^, D. 

 aculeata, etc., he had observed the beautiful form described by the 

 English naturalist. Dr. Wallich, under the name of D. corona. 

 The shell of this species resembles a Roman helmet, with 

 from five to seven spines, and it has the mouth notched with 

 twelve serrations. A comparatively large species observed may 

 be peculiar, though future investigation may prove it to be only a 

 variety of 1). lageniformis. The shell has the form of an ancient 

 amphora, without the handles, and it measures the fourth of a 

 line in length. With its delicate pseudopods of varied form, 

 and sometimes extending far bej^ond the length of the shell, it 

 appears as a microscopic vase of phantom plants. 



Among Amoeba he had observed one which he suspected to be 

 the same as A. princeps of Ehrenberg, but it was twice the size 

 given by this author. It was remarkable for its activity and 

 wonderful changes of form. At first globular, the next moment 

 pseudopods appear like a multitude of dewdrops all over the sur- 

 face. A few of these stream forth and widen in their course, 

 while others disappear. The animal will then extend itself and 

 appear like a branching coral. At one moment it will enter and 

 traverse the interstices of a mass of mud and sand, and then 

 emerge without an adherent particle. Detached and floating it 

 will appear like a long-rayed star. At times it assumes the most 

 grotesque forms that of a human head with a rapidly growing 

 nose ; the outline of an elk with the antlers extending, or a leg 

 elongating at the expense of the body. The species is common 

 in the vicinity of Philadelphia. First observed in the neighbor- 

 hood of Swarthraore College, it was also found in the ditclies of 

 the Neck below the city. The animal contained a multitude of 

 minute particles of ellipsoidal form which reminded him of the 

 discoliths of the Bathybins of Prof. Huxley. 



It is an interesting question whether our fresh-water protozoa 

 have reached us from the same sources as those of Europe and 

 other remote countries. If derived from the same sources they 

 were probably infused in the waters of the different continents at 

 an early age when the latter were not separated by ocean barriers. 

 If thus early infused we have a remarkable instance of a multi- 

 tude of specific forms retaining their identity through a long- 

 period of time. Such a view might appear to oppose the 

 doctrine of evolution, but not justly so, for the simplest forms 

 would be the slowest or least likely to vary, while the most com- 

 plex, from their extended relationships, would be most liable to 

 variation. Perhaps, however, the simplest forms of life, of the 

 same species, may have originated independently of one another, 

 not only in different places, but also at difl'erent times, and may 



