8 THE AMERICAK MONTHLY [January, 



Heliozoa forming the fii^st, the Radiolaria (represented mainly by the Poly- 

 cistina) and the Foraminifera forming the second section. It would carry us 

 too far to enter into the minor classifications of the marine Rhizopods, but 

 the fresh-water forms require more extended notice, as they constitute what 

 are generally meant by the term ; what, I take it, we are all most interested 

 in as objects of study and discussion ; and what. I presume, the members of 

 this society expected to be described in a paper on this subject. Therefore, 

 simplv begging you to bear carefully in mind that the Foraminifera and the 

 Polycistina are just as truly Rhizopods as the fresh-water forms commonly 

 suggested by the name, I pass on to the latter. 



The fresh-water Rhizopods then fall, as we have seen, into two groups — 

 the Protoplasta and the Heliozoa. But of these, the former is much the larger, 

 and also the more important, systematically considered. For while, under 

 the head of the Heliozoa, or sun-animalcules, Leidy describes some 8 genera 

 (excluding Vampyrella, which is now placed by Carpenter in a still lower 

 division of the Protozoa) under the head of the Protoplasta he enumerates 

 22. Again, all those 8 have such a marked feature in common that when 

 one has seen one he may be said to have seen all ; at least, he would have 

 no difficult}' in placing anv of them at once. A glance at the names suffices 

 to show this, thus : — 



Actinophrys, Heterophrys, Raphidiophrys, Diplophrys, Actinosphajrium, 

 Acanthocystis — that is to say, all these are characterized by radiating- fila- 

 ments from all parts of the body. Actinophrys sol, therefore, the common 

 sun-animalcule, needs onlv to be well studied to familiarize the observer with 

 this whole order, the 8 genera of which are founded upon the peculiar form 

 of the rays. Furthermore, one of these, Clathrulina, is the only fresh-water 

 rhizopod which bears a stem, and Hyalolampe is so rare that it need not be 

 taken into account. The order is thus practically reduced to the 6 genera 

 mentioned, so far as the student is concerned, all of which, as we have said, 

 may be recognized at once ; while as to the distinct genus, rays forked, not 

 forked, diverse, long and needle-shaped, or extending in tufts from two ori- 

 fices, — these are all the points necessary to bear in mind to distinguish respec- 

 tively Acanthocystis, Actinophrys, or x\ctinosph£erium, Heterophrys, Raphi- 

 diophrys, and Diplophrys. 



Thus you will see that the study of the Rhizopods, as regards minute classi- 

 fication, narrows down to the study of the first order only. The Foraminifera 

 and the Radiolaria may be omitted as tnarine^ and therefore better fitted for 

 separate investigation ; and the Heliozoa are so similar as to occasion no 

 difficulty. 



We come then to the Protoplasta as the order of all four which especially 

 demands our consideration, because it is greatest in the number of genera, and 

 because these genera present such wide diversity of form. 



Here, again, Leidy makes a division which helps us not a little, by separat- 

 ing the protoplasta into two sub-orders, namely, the Lobosa and the Filosa, 

 the former with blunt finger-like processes, the latter with thread-like pro- 

 cesses of gixat delicacy. Under the head of Lobose Protoplasts we have 13 

 genera, of Filose Protoplasts 9. Let any one then look at the shape of the pseu- 

 dopods as they are extended from the body of the creature, and he will be 

 able to rule out at once either 13 or 9 of the genera, as the case may be. Sup- 

 posing that he has thus succeeded in localizing his specimen in the Lobose 

 sub-group, there is another point which will simplify the identification still 

 further. Has the creature a shell or not? If not, he may exclude 8 of the 

 13 genera of this division, and place it confidentlv among the first 5, all of 

 which are amoeboid in character and readily distinguished, namely : — Ann^ba, 

 Oiiramceba. Dinamceba. Pelomyxa. Hyalodisctts. Of the whole five iVmoeba 



