310 
POPULAR SCIENCE REVIEW. 
statoblasts, closely resembling Allman\s figure of Plumatella 
emarginata ; the other was unlike any figure in that gentle- 
man’s monograph. 
According to Dr. Fritz Muller ( u Archiv fur Naturgesch.” 
I860, p. 312), there exists in some of the marine members of 
this group a colonial nervous system, in addition to the individual 
nervous system alluded to above. By means of this colonial 
system the movements of the general body are controlled. It 
is quite probable that careful microscopic examination may re- 
sult in the discovery of a similar organization in Cristatclla, and 
other fresh-water species. 
EXPLANATION OF PLATES XIII. AND XIV. 
Plate XIII. — Figs. 1 and 2. Plan of a Polyzoon : (1) exserted, (2) retracted 
Fig. 1. a, mouth and tentacles ; b, alimentary canal ; c, anus ; d, nervous 
ganglion ; e, investing sac ; f, /', reproductive organs ; g, retractor 
muscle. 
Fig. 3. Cristatclla Mucedo. 
Fig. 4. Plan of an Ascidian Tunicate, a, triple investing sac ; g, respiratory 
apparatus ; n, mouth ; o, (Esophagus ; p, stomach ; q, intestine ; 
r, anus ; u, nervous ganglion ; v, heart. 
Fig. 5. Plan of a Fresh- water Polyzoon, showing homologous parts with 
Fig. 4. For explanation, see Fig. 1. Figs. 1, 2, 4, 5, after Allman. 
Plate XIV. — a, Plumatella repens , attached to a stone (natural size) ; b, 
statoblast of ditto ; c, ditto of P. fruticosa ; d, ditto of Cristatclla ; 
c, ditto of Frcdericella Sultana ; (all magnified). 
