OBSERVATION OX FKESH-WATEK I'OLYZOA. 



119 



wall, and the outer cell-layer and the lining epithelium are clciirly 

 distinguishable from each other, a.s at (jther places, although no 

 muscular layer intervenes between them. At this place, the cells uf 

 the outer layer are wanting in vacuoles and both layers stain more 

 deeply than anywhere else. The area is comparable to the growing 

 point in plants. How the buds arise, shall be treated under a s[)ecial 

 chapter later on. 



B. Reproduction. 



In fresh- water Polyzcja, reproduction may take place sexually or 

 asexually in three ditferent ways, as tabulated below : 



[Reproduction by 



Xature : 

 Function 



iSTevv individual 

 originates from : 



The number of 

 body-layers that 

 enter into the 

 formation of the 

 new individual : 



1 

 Ovum 

 sexual 



2 I 3 



Statobhist BuddinjT 



asexual 



to form primary poly_ 

 zooid irivinii' rise to 

 a new colony. 



to form a nundjer 

 of new polyzooids, 

 thus increasing the 

 extent of a colony. 



one 

 cell 



one 



many cells 



two. 



13y the first nuxle, an ovum should undergo segmentation, and 

 passing through a series of metamor[)hosis give rise to a new primary 



