FRESH-WATER ALG. 269 
similarities to many species of infusorial animal- 
cules, and exhibit the same spontaneous move- 
ments; and even in their elementary composi- 
tion they are identical with some of the lowest 
members of the animal kingdom. In these primi- 
tive plants and animals, we may fairly enough 
conclude that the animal and vegetable kingdoms 
pass into each other ; they form the one common 
base or point from which these two systems of life 
start, to recede so widely from each other in the 
large and complicated organizations which stand 
at the head of both. ‘From man to the primary 
animal and vegetable cell, Schmidt justly ob- 
serves, ‘there exists no gap in the realization of a 
general idea upon which nature as a whole is 
based. There is no abrupt transition from one 
kingdom to another, but an insensible gradation. 
Thus the embryo germ of an alga or sea-weed is 
identical, in elementary composition and form, 
with that of a medusa or ascidia ; in the former we 
have the higher stage of development of the plant, 
in the latter the simpler form of the animal’ The 
vegetable nature of the Diatoms is, however, I 
think, clearly indicated by the marked results of 
the application of the spectroscope to them. The 
spectrum of dzatomin or the olive-yellow endo- 
chrome of diatoms is absolutely identical with that 
of chlorophyll or the green endochrome of plants. 
