53 



•protozoa seem to offer an especially favorable mater- 

 ial for investigation. Among others, the investigations 

 of Maupas-i- throw light on many points of the question 

 interesting iiQ, In starvation cultures very numerous 

 dwarf specimens arise, since the organisms alv;ays divide 

 before they are "fully grown". At the same time, the 

 processes of differentiation talking place in normal cells, 

 are partially "arrested"; the cilia, the undulating mem- 

 branes, indeed the mouth parts, are either not developed 

 at all, or only to a reduced size. (Compare above p, 37) . 



In higher animals, and especially in man, incomplete 

 tissue differentiations, corresponding to the hypoplasias 

 above described, appear only rarely, at least, the patho- 

 logical literature which I knov/ throws only scanty light 

 on this. As a well-known example, I will name the bones 

 in rhactitis, in ?/hich the histological characters of the 

 cattilage are retained longer than in normal bones. 

 Further, tissue hypoplasia is present if succulent epithe- 

 lial layers do not hornigy,- and the like. 



1. Compare for example, Sur la multiplication d. 

 infusoires cilies. Arch. zool. exp. et gen. 1888, 2me, 

 ser, , T. YI. 



