40 SEAWEEDS 
great external differentiation of form and consider- 
able internal differentiation of tissue, as well as 
others consisting of a mere row or plate of similar 
cells. The sub-class may be regarded as a fairly 
natural assemblage of orders easily to be distin- 
guished from the other sub-classes, though it includes 
such diverse types as (1) the Fucacew, of which the 
unciliated oospheres, many thousand times greater 
than the antherozoids, are produced like the latter 
in definite conceptacles, from which they are ex- 
truded ; (2) the Cutleriacew, possessing non-sexual 
zoospores, and ciliated oospheres (or 9 gametes) 
many times larger than the antherozoids (or ¢ 
gametes)—the oospheres, however, being incapable 
of fertile union until they have come to rest— 
neither borne in conceptacles; and (3) other orders 
possessing ciliated gametes of equal or nearly equal 
size, In one case (Splachnidiacew) borne in con- 
ceptacles, in the others within external mother-cells. 
It would be doing violence to a natural system 
of classification to accept the proposed inclusion of 
the Diatomacew among the Phwophycee on the sole 
ground of colour. This order is of a distinctly 
aberrant character, and shows no morphological 
point of contact with even the lowest groups of 
Pheeaphycee. 
FUCACE. 
Gencral Characters.—The distinctive characters of 
the Fucacee are the production of unciliated 
oospheres in oogonia and antherozoids in antheridia, 
