152 Book Notices. 
ties, such as Renilla, Pennatula, etc., among Polyps, and all the Sipho- 
nophore among Acalephs, we must still further distinguish another kind 
ing frequently of one or two spheromeres more usual, sometimes, 
yen, of dou rmal number, or of a few less nd yet, year alter 
year, the same Discophore reappear upon our shores, with the same 
range of differences among their individuals, Among Hydroids poly- 
morphism prevails to a greater or less extent, besides the differences 
arising from sex. Few species have only one kind of individuals. 
there are generally at least two kinds of Medusw in one and * 
same community. But notwithstanding this polymorphism among 2 
individuals of one and the same community, genetically connected 1° 
gether, each successive generation reproduces the same kinds of heter 
ogeneous individuals, and nothing but individuals linked together in the " 
same way. Surely we have here a much greater diversity of individe- : 
th t 
als, born one from the other, than is exhibited by the mos dive 
breeds of our domesticated animals; and yet all these heterogent® = 
individuals remain true to their species, in once case as In the oN 
and do not afford the slightest evidence of a transmutation of speed, 
ould the supporters of the fanciful theories lately propound . 
only extend their studies a little beyond the range of domesticate fete 
als, would they investigate the alternate generations of the Acaleph 
