38 FRESH-WATER RHIZOPODS OF NORTH AMERICA. 



of the endosarc proceeds from the interior of the body, and is continuous 

 through the axis of the latter, back of the source of the pseudopod ; and if 

 this forms the fore part of the body, the current may be continuous its entire 

 length. If a growing pseudopod proceeds from an intermediate position, 

 currents of endosarc may flow from opposite directions to promote its 

 extension. 



The flow in the current of endosarc is always most active axially, both 

 within the body and the pseudopods. As it approaches the end of a 

 pseudopod, formed by the advancing ectosarc, it usually enters to one side 

 and turns upon itself, as represented in fig. 11, pi. II. 



New pseudopods start more or less abruptly, and give one the impres- 

 sion as if they proceeded from a sudden escape of a portion of the contents 

 of the body, through an accidental rupture of its surface. In their extension 

 they appear to flow onward like a liquid stream, as previously intimated, 

 always preceded by a portion of the clear ectosarc, followed by an inces- 

 sant influx of the endosarc. In the precedence of the ectosarc, it looks 

 as if it were a clear liquid, incessantly drained from the endosarc, and 

 flowing off in a stream; but apparently before the ectosarc has a chance of 

 accumulating to any considerable extent, it is constantly followed by 

 granular endosarc, as if this was forced into it from behind by contraction 

 of the body. 



The progress of the animal may continue steadily for a time, induced 

 by the equally steady extension and advance of one or more pseudopods, 

 accompanied with a more or less brisk flow of the endosarc of the body, 

 continuing in one stream, or dividing into several, according to the number 

 of the advancing pseudopods. 



While there is no absolute distinction between the ectosarc and endo- 

 sarc, the two being continuations of the same protoplasmic mass, in the 

 movements of the animal the endosarc appears to flow within walls, more 

 or less thick, formed by the ectosarc. With the exhaustion of the endosarc 

 from behind, the including ectosarc contracts, and melts away into the 

 advancing portion of the body. 



Ama'ba proteus, while steadily pursuing its course, may slacken its 

 speed and altogether cease its onward movement ; and after a brief interval, 

 a new pseudopod may start forth, and with its extension in the same direc- 

 tion the course of the animal may be entirely changed from the former one. 



