24 FRESH-WATEE EHIZOPODS OF NORTH AMERICA. 



In the Lobose Protoplasts, more than in any other Rhizopods, the sar- 

 code mass of the body exhibits a tendency to differentiate an exterior, 

 usually more consistent layer of protoplasm, which, though actually con- 

 tinuous with the interior, ordinarily more fluent protoplasm, seems like an 

 investing membrane, preventing the escape of the latter. For convenience, 

 the two portions of protoplasm, differently related in position, have been 

 appropriately termed the Endosarc and the Ectosarc (Gr cndon, within ; 

 elrtos, outside ; sarx, flesh). 



The ectosarc appears as the exterior clear protoplasm ; the endosarc 

 as the interior granular protoplasm, though high powers of the microscope 

 generally reveal an infinitely fine granular constitution also 1o the former. 



Dr. Wallich regards the endosarc and ectosarc as temporarily distinct 

 portions of the sarcode, mutually convertible into one another. The ecto- 

 sarc becomes differentiated from the endosarc by contact with the outside 

 medium in which the animal lives, and from time to time reverts again to 

 the condition of the more fluent endosarc within. 



From this view, as intimated by Dr. Wallich himself, the ectosarc is 

 due to a temporary and partial coagulation of the endosarc coming into 

 contact with the water in which the animal lives, and again reverts to the 

 condition of the more fluent endosarc as it retreats to the mass of the latter 

 within the body. The process reminds one of the cooling of a molten mass 

 of metal at the sides of a crucible, and the melting-away again of the crust 

 as it is stirred from the sides into the remainder of the molten mass within. 



In the movements of the sarcode mass of the body, as exemplified in 

 an Amoeba, a temporary increase of the ectosarc may occur in one or 

 more positions, accompanied with a proportionate flow or drain of hyaline 

 protoplasm from the contiguous endosarc A reduction in thickness of the 

 ectosarc follows an absorption of the clear protoplasm among- the more 

 visible granular constituents of the endosarc. 



The pseudopods of the Lobosa commence as projections of the clear 

 ectosarc, and may continue as such in their extension unless unusually pro- 

 longed or thick. In the latter cases they are accompanied to a variable 

 extent with an influx of the endosarc. They are mostly digitiform or 

 finger-like processes, or, in other words, are cylindrical, with rounded ends, 

 variable in number and length, often simple, frequently more or less 

 ramose, but almost never anastomosing. Sometimes they are pointed, and 



