154 SEAWEEDS 
there are borne the fertile whorls, each with a 
secondary whorl and a terminal sporangium in the 
middle. The ultimate whorl of these lateral 
branches, overtopping the sporangia, form a kind of 
cortex (as in the last genera), but without definite 
facets externally. The space between them and the 
axial cell is originally of slimy consistence, but 
becomes the seat of incrustation. At the joints 
there are no fertile whorls and the lateral branches 
are here simple and decrease in length from 
below upwards. It is a similar formation which 
bears the terminal tuft of hairs. No observation of 
germination has been made. 
A number of fossil genera, such as Decaisnella, 
Haploporella, Dactylopora, Dactyloporella, Uteria, 
and Polytrypa from the Eocene, and Munieria, 
Gyroporella and Triploporella of Cretaceous age are 
certainly nearly related to the forms just described. 
The Reproductive Organs.—Dasycladus is the only 
genus in which the gametes have been observed. 
We have seen that in Acctabularia the gametes 
unite only with those from other gametangia, but in 
Dasycladus the matter is carried a step farther, since 
the gametes are here incapable of conjugation with 
others from the same plant, and indeed they conju- 
gate only with those of particular plants, not with any 
other indiscriminately. It appears from this obser- 
vation that though these gametes are apparently 
all alike, there yet resides within them a definite 
character indicating a difference of sex, though this 
is not determinable by us from their structure. 
Judged by itself alone, Dasycladus appears to pre- 
