98 ON THE ORIGIN AND [CHAP. 



sent the prirriaeval ancestor from which these more 

 highly-developed types have been derived, and which, 

 in spite of their great antiquity in spite of, or perhaps 

 in consequence of, their simplicity, still maintain 

 themselves almost unaltered. 



Thus the form which Haeckel has described 1 under 

 the name Protamceba primitiva y PL 5, Fig. I 5> con- 

 sists of a homogeneous and structureless substance, 

 which continually alters its form ; putting out and 

 drawing in again more or less elongated processes, 



FIG. 59, Prorhynchus stagnalis.~ 



and creeping about like a true Amoeba, from which, 

 however, Protamceba differs, in the absence of a 

 nucleus. It seems difficult to imagine anything 

 simpler ; indeed, as described, it appears to be an 

 illustration of properties without structure. It takes 

 into itself any suitable particle with which it comes in 

 contact, absorbs that which is nutritious, and rejects 

 the rest. From time to time a constriction appears at 

 the centre (PL 5, Fig. 2), its form approximates more 

 and more to that of an hour-glass (PL 5, Fig. 3), and 

 at length the two halves separate, and each commences 

 an independent existence (PL 5, Fig. 5). 



In the true Amcebas, on the contrary, we find a 



1 Monographic der Moneren, p. 43. 



2 Gegenbaur. Grund. d. Vergleich. An at. p. 210. See also 

 Da:. M. S. Schullze, Beitrage zur Naturg. der. Turbellarien. 1851. 

 PL vi. fig, i. 



