59 2 Church. — The Structure of the Thallus of 
sphere-crystals, and is especially noticeable in the cortical 
segments of Stage IV. Calcification becomes more pro- 
nounced, and is remarkable for its limitation to definite areas 
(Fig. 24) ; but it never reaches the massive incrustation of 
N. Kelleri. The layer beneath the dilated ends of the 
cortical segments becomes much thickened and forms a con- 
tinuous calcareous jacket, perforated by the slender non- 
calcified pedicel-portions of the cortical segments ; a small 
deposit is laid down on the basal segments ; the main axis, 
growing-point, surface of the thallus, and filamentous portions 
of the appendages do not incrust ; but the aplanosporangia 
are densely coated to a distance more than half-way down 
their pedicels (Figs. 24, 30). 
Relation of N. dumetosa to the rest of the Dasycladaceae. 
From the observations above recorded on the youngest 
plants available, it may be reasonably concluded that 
N. dumetosa commences its life-cycle as an organism pre- 
senting the appearance of a Vaucheria ; that is to say, 
a coenocytic filament without transverse septa, possessing 
a dichotomously-lobed rhizoid portion, and exhibiting a 
general tendency to form branches at right angles to the main 
axis and equal to it in diameter. This continues only for 
a length of two or three millimetres, when the whorled 
Dasycladus type is suddenly assumed. A similar filamentous 
stage has been shown by De Bary to occur in Acetabidaria 
mediterranea ; N. dumetosa , however, is more precocious in 
development than this Acetabidaria , which reaches a length of 
over 20 mm. before growing the first whorl of appendages, 
and thus agrees with the youngest stage observed in N. annu- 
lata by Solms-Laubach. 
After the definite assumption of the whorled type of growth, 
the study of the development of N. dumetosa resolves itself 
into a question of the variation in form, number, and com- 
position of certain lateral appendages. 
Reviewing the different stages of growth, I think it will be 
